Not "all" of them.

No, not all of us. As AntigoneRising correctly stated, the so-called “special underwear” is actually called a “temple garment”; however, I’ve never known a Latter-day Saint to refuse to discuss it, if someone has an honest and respectful question about it. In short, one of the most important parts of temple worship is the ordinance of the endowment. As part of this ordinance, we make sacred covenants with our Father in Heaven—for example, to keep the law of chastity (i.e. no sexual relations with anyone besides one’s own legal spouse). The garment is a physical, near-omnipresent reminder of those covenants. HTH!

Good Mormons do. But you won't hear it from their lips, nor will they discuss it. And they will contradict everyone who DOES talk about it. Now watch the negging.

My understanding of Mormonism is that there is some form of special temple garments they wear (I don't know whether or not they have to, or why they do / don't choose to wear them, I merely know that they exist). They are only referred to 'special underwear' jokingly / mockingly by people outside of the church, that I know of, no one inside would call them something like that ; )

Glenn has done a great job explaining what needs to be explained without getting into the heavy details. That's for someone to understand later when they've made more of a spiritual commitment to find out not because of mere curiosity but out of a genuine desire to know the Lord. That's ultimately why we go to the temple...to get the depth of teaching that the Lord reserves for those who are obedient, humble, and spiritually mature enough to receive it. The garment is incidental to those teachings. It is an outward reminder, and yes, it is important, but is not the sole focus of why we go to the temple. Worshiping God is the reason we go. Like I always say to people who ask me in hushed, timid tones why we keep so many "secrets": There are no secrets! Only sacred things that are not discussed in mixed company. Just like I don't go telling the whole world about my family's private matters, I don't make a habit of shouting out to the world those deeply personal, spiritual inspirations and revelations that I've learned in the temple that are really only between God and me. Anyone and everyone who sincerely wishes to be baptized and make the same covenants with God that other LDS members do is certainly welcome to do so! No secrets! http://americantestament.blogspot.com

The "special underwear" is properly called the "temple garment". It is made of ordinary material and has no apparent special powers. As it's name implies, only Mormons who have received their "endowment" (eg. gone through the temple) wear the temple garment. It is a reminder of the covenants made in the temple.

haha It's not really "special underwear" and no not all Latter Day Saint's wear garments. Although, many do. They are called Garments and they are an outward expression of an inner commitment to God. Usually obtained by performing special odrinances in the Temple. Like getting your Endowments by serving a mission or marraige. They are encouraged to be worn but by no means required.

Absolutely not, that is strickly for temple mormons, those that were sealed in the temple, my Great Grandparents were temple Mormons & wore the Mormon garb, 24 hrs a day, even bathed with it on.

Are you wearing it when you are baptised? The Wikipedia site that AR linked above says: "The garment is worn by adult adherents who have taken part in an ordinance known as washing and anointing, usually in a temple as part of the Endowment ceremony. The temple garment is also known by other names: the garment or garments, or (in the broader community) "Mormon underwear".[2][3] In modern times, temple garments are worn primarily by members of The Church of Jesus Christ of Latter-day Saints (LDS Church) along with several small religious groups who separated from the LDS Church. Adherents consider them to be sacred and may be offended by public discussion of the garments." I can't understand why the Masonic symbol is on a religious garment. The connection between Mormons and Masons has been explained away by LDS apologists but that makes me think of the U.S.Navy building shaped like a swastika. When they were building it in 1967, they knew they shouldn't use the shape but they did anyway. Now, after widespread protest from citizens, they'll have to pay $600,000 to change the shape. It has taken many explanation from Mormon writers and thinkers to give reasons for the underwear symbol (as well as many, many Masonic symbols in Mormonism). But like the swatika building, people still say "What were they thinking!?

You've already received a plethora of great answers on this one so all I can do is hope to expand lightly on what's already been said and hopefully include some new information that has been NOT said. Only "Temple Mormons" - those who have been through an endowment ceremony - wear "Temple Garments". Generally speaking this is about 20% of active Latter Day Saints. There's a process that's required for being "Temple Worthy" that includes answering the following set of questions: TEMPLE RECOMMEND QUESTIONS: 1. Do you believe in God, the Eternal Father, in his Son, Jesus Christ, and in the Holy Ghost; and do you have a firm testimony of the restored gospel? 2. Do you sustain the President of The Church of Jesus Christ of Latter-day Saints as the prophet, seer, and revelator; and do you recognize him as the only person on the earth authorized to exercise all priesthood keys? 3. Do you sustain the other General Authorities and the local authorities of the Church? 4. Do you live the law of chastity? 5. Is there anything in your conduct relating to members of your family that is not in harmony with the teachings of the Church? 6. Do you affiliate with any group or individual whose teachings or practices are contrary to or oppose those accepted by The Church of Jesus Christ of Latter-day Saints, or do you sympathize with the precepts of any such group or individual? 7. Do you earnestly strive to do your duty in the Church; to attend your sacrament, priesthood, and other meetings; and to obey the rules, laws, and commandments of the gospel? 8. Are you honest in your dealings with your fellowmen? 9. Are you a full-tithe payer? 10. Do you keep the Word of Wisdom? 11. Have you ever been divorced or are you now separated from your spouse under order of a civil court? If yes, (a) - Are you current in your support payments and other financial obligations for family members, as specified by court order or in other written, binding commitments? (b) Were there any circumstances of transgression in connection with your divorce or separation that have not been previously resolved with your bishop? 12. If you have received your temple endowment -- (a) Do you keep all the covenants that you made in the temple? (b) Do you wear the authorized garments both day and night? 13. Has there been any sin or misdeed in your life that should have been resolved with priesthood authorities but has not? 14. Do you consider yourself worthy in every way to enter the temple and participate in temple ordinances? Link to source = http://www.concernedchristians.com/index.php?option=com_fireboard&Itemid=42&func=view&id=47545&catid=519 FYI, I believe that these questions are circa 1995-ish so they may be slightly different now. Perhaps a member who's also a Mormon Bishop can "freshen" the list for us if it's now dated. Anyhow, if your Bishop feels that you're "Temple Worthy" based on this interview you will then receive a Temple Recommend - I have provided an image of one below. You show this at the LDS Temple and can then proceed to your particular Temple Ceremony. Typically Melchizedek Priesthood Endowments for men, Marriage Endowments for women (and men of course), and Proxy Baptism for the Dead for either or. So you can see LDS Temples are busy places! And, as so many others have stated, the garments are considered a perpetual reminder of the vows and covenants that the Temple Mormon makes in the LDS Temple. Barring unusual circumstances they are to be always worn. And just so you understand how much BETTER things have gotten for Latter Day Saints regarding Temple Garments I've also provided an image of their evolution across history. One can only pity those poor early Temple Mormons! If you would like to learn more about LDS Temples from an outside perspective please consider the following portal page that I've created on the topic via this link: http://www.concernedchristians.com/index.php?option=com_fireboard&Itemid=42&func=view&id=70880&catid=512#70880 By the way, it's well documented that the LDS Church greatly inflates it's membership numbers, but that's a question that hasn't been asked so I'll just refer you to these links if you're interested in discovering why I can make such a bold, brash statement: http://www.concernedchristians.com/index.php?option=com_fireboard&Itemid=42&func=view&id=75079&catid=10 http://www.concernedchristians.com/index.php?option=com_fireboard&Itemid=42&func=view&id=75644&catid=527#75644 http://www.concernedchristians.com/index.php?option=com_fireboard&Itemid=42&func=view&id=78863&catid=523