Structured interviews and focus group discussions were conducted among 834 young Thai men drafted into military service by random lottery in northern Thailand. Level of AIDS risk, exposure to AIDS information, level of knowledge about AIDS, and perception of risk for acquiring HIV and AIDS were assessed at baseline and six months after induction into the Army in 1991. General fear of AIDS was high, yet personal perception of risk for acquiring HIV was low, even for those at enhanced behavioural risk of infection with HIV. Multivariate PATH analysis shows that exposure to information about AIDS significantly reduced risk taking from baseline to follow-up, but only by first affecting personal risk perception. Focus group discussions revealed that risk perception for acquiring AIDS was low due to never knowing a person with AIDS, because prostitutes had health certificates for STD, and since many believed that AIDS could be cured or prevented with folk medicines. Implications and recommendations for intervention programmes are discussed.