During the summer of 1977, an epidemic of rubella occurred among adults in Hawaii. The highest attack rate was in women 20-24 years old (226/100,000), with almost total sparing of young schoolchildren. A case-control investigation implicated a specific discotheque as a common place of exposure for persons with onset of disease during the epidemic peak (chi 2 = 12.9,p less than 0.001). A piano player/singer at the discotheque was the apparent source of the virus transmission. The large number of cases linked to this musician suggests that airborne transmission occurred while he was singing rather than by direct person-to-person contact. Rubella vaccine was given to 6523 women in public clinics held during the epidemic. Despite screening for pregnancy and birth control usage, 23 women (3.5/1000) became pregnant within three months after receiving the vaccine. Eleven of 12 women who reportedly contracted natural rubella while pregnant elected to terminate their pregnancies; the 12th had a normal appearing infant. The susceptibility rate for all adults tested for rubella hemagglutination inhibition antibody was 36.9%, a rate similar to the found in earlier surveys in Hawaii. The occurrence of this epidemic confirms the changing epidemiology of rubella with respect to age distribution and supports the view that vaccination of young children may not be sufficient to protect adult women from exposure to rubella, especially in areas where a high proportion of adults remain susceptible.