Currently astronauts do not have appendectomies before missions. The idea has been considered for future long-duration space missions such as missions to Mars. The estimated incidence of appendicitis in a crew of 6 (ages 35-50) on a long-duration space mission is 1 case every 125 yrs based on the incidence in the same age groups in the general population on earth. If analog environments are considered, the estimated incidence may be higher. For example, the incidence of appendicitis in polar environments is higher than that in the general population. Using polar environments as an analog for spaceflight, the incidence of appendicitis may be 1 case per 9.5 years or even higher. It is hypothesized that the increased incidence in polar environments is due to increased stress and immunodepression. Space travel is also stressful and immunodepression has been documented in some astronauts in some studies. Prophylactic appendectomies are performed on over-wintering physicians at some Antarctic bases. This was initiated after physicians who developed appendicitis needed to be evacuated at great expense. One Soviet physician, Rogozov, was unable to be evacuated and was forced to perform an appendectomy on himself using local anesthesia. Prophylactic appendectomies were proposed for German submarine crews during WWII. As recently as April 2004 it has been reported by Russian television that cosmonauts have prophylactic appendectomies along with removal of any imperfect teeth. This is not true. Appendicitis has never occurred in astronauts or cosmonauts during spaceflight. It was suspected on several Salyut missions, but the diagnosis turned out to be different - nephrolithiasis and prostatitis??? Appendicitis has occurred in at least one (possibly two) cosmonaut candidate shortly before flight. She was replaced on the mission. There have been only two cases of appendicitis in astronauts on the ground. If appendicitis does occur in long-duration spaceflight, evacuation is unlikely to be an option. In such situations, appendicitis can often be managed non-operatively using antibiotics. Antibiotics have been used on US submarines since 3 appendectomies by pharmacists mates using non-surgical instruments in WWII, the first on the USS Seadragon by Wheeler B. Lipes. Antibiotic usage can be supplemented by percutaneous drainage of any abscess. This capability has not existed on submarines, but it has been shown to be feasible in a weightless environment. Appendicitis treated non-operatively may recur, but the treatment may buy enough time to return to earth for an interval appendectomy. Surgery may be possible on long-duration space missions. It has been performed on animals in parabolic flight, underwater, and on the shuttle. There are many issues left to resolve before it can safely be considered for humans. There are also issues regarding the diagnosis of appendicitis in a weightless environment. The classic site of maximal tenderness, McBurney's point, may change in location, possibly shifting cefalad (since the appendix is no longer pulled caudally by gravity) as it sometimes does during pregnancy. Ultrasound is currently available on the ISS. CT is not -- too heavy, requires too much power, extra radiation exposure for patient and crewmembers, too difficult to maintain, and images may be affected by increased background radiation of space.