Two hundred eighty-one Hmong, 240 Mien, and 210 Lahu hill tribe people (ages between 17-39) in northern Thailand were interviewed from March to May 1996 about their knowledge, beliefs, attitudes regarding AIDS, STDs and condoms, and sexual behavior, to guide future tribal AIDS education and care programs. Premarital sex for both men and women and extramarital sex for men seems to be still culturally permissive and wide-spread among the Hmong and Mien people. The Lahu reported lower cultural acceptance, but this group had higher levels of premarital and extramarital sex than the other two groups, excepting extramarital sex for Hmong men. Many men among the three groups knew about condoms, but they do not like to wear condoms because, "it is not natural." Lahu people had the least education, were the least literate, and had the least family income. In addition, Lahu had the lowest level of knowledge of AIDS and STDs and they seem to have the most risky behaviors among the three groups. On the other hand, although Mien people had the highest education, were the most literate, had the most family income, and had the highest level of knowledge of AIDS and STDs, they seem to have high risk sexual behavior, also. There were increasing numbers of hill tribe people migrating to the cities and becoming involved to a greater degree in seasonal or permanent wage labor, including the commercial sex industry among Lahu and Mien groups. Hmong seem to have the lowest number of workers migrating to the cities. The results indicate the need to inform and educate tribal people about AIDS in a socio-cultural specific context.