There are two theories of which I know. The first one states that European explorers found the animal in the South American country of Guyana. The other one states that the explorer brought them back to Europe and sold them for one guinea. The pig part likely comes from these explorers thinking they resembled small pigs. Either way, there doesn't seem to be any absolute explanation.

Actually, they come from New Guinea. Since they are native and run wild like the boars we have here, they were dubbed Guinea Pigs. They are also a good source of protein for these peoples diets and were usually cooked on a spit over a fire.

Whatever the reason, this perception of pigginess occurred in many languages other than English; the German word for them is Meerschweinchen, literally "Little Sea Pigs" (sailing ships stopping to reprovision in the New World would pick up stores of guinea pigs, which provided an easily transportable source of fresh meat), the Russian and Polish word for them is similar, "morskaya svinka" and "winka morska" respectively, meaning also "Little Sea Pig" (it comes from archaic use of the word to mean "overseas"). The French word is Cochon d'Inde, (Indian pig), the Dutch used to call it guinees biggetje (Guinean piglet), and in Norway, Sweden and Denmark they are called marsvin (a combination of the Latin word mare for ocean, and Norwegian/Swedish/Danish svin which means pig). In Greek they are called 'indika xoiridia' (Small Indian Pigs), and in Portuguese, the term is "porquinho da Índia", literally "little pig of the Indies". In Italian the term is either "Porcellino D'India" (Little Indian Pig) or "Cavia Peruviana" (Peruvian Cavy). However, this perception of pigginess is not universal to all languages or cultures. For example, the common Spanish word is 'conejillo de Indias' (Indian bunny rabbit). The scientific name of a common species is Cavia porcellus, with porcellus being Latin for "little pig". The origin of "guinea" in "guinea pig" is even harder to explain. One theory is that the animals were brought to Europe by way of Guinea, leading people to think they had originated there. Another theory suggests that "Guinea" in the case of the guinea pig is a corruption of "Guiana", an area in South America. A common misconception is that they were so named because they were sold as the closest thing to a pig one could get for a guinea (an old British coin with a value of 21 shillings, or 1.05 GBP in modern decimal currency). However, evidence does not support this conjecture: for example, the Dutch name refers to the country of Guinea rather than the British coin, and the first guinea pig was described in 1554 by the Swiss naturalist Konrad Gesner more than a hundred years before the first guinea was struck. http://en.wikipedia.org/wiki/Guinea_pig

i thought explorers found them in new guinea and thought from first sight they were baby pigs/ bores

I read in a book that they are called guniea because when they were brought to England and sold they cost a guniea...and the pig part is obvious because of the noises the make when excited or scared or happy :)

I have my own statement as to why I think they are called Guinea PIGS. They are pigs in one respect, they eat all day! I also heard they were sold for one guinea :)

Everyone here is stupid. They are called guinea pigs because they have italian accents.