This study assessed general knowledge of AIDS, beliefs about preventing AIDS, and sexual behavior among two groups of male adolescents at high risk of HIV/AIDS: 60 sexually delinquent males and 57 non-delinquent runaway males. Significantly fewer sexually delinquent than non-delinquent (runaway) males had experienced sexual intercourse with a consenting female partner (45 vs. 89 per cent). Sexually delinquent youths scored significantly lower than non-delinquent youths in general knowledge of AIDS (65 vs. 73 per cent) and were not able to discriminate safer behaviors from those which were less safe (42 vs. 71 per cent). Both groups reported moderate support for beliefs about preventing AIDS. These results suggest HIV/AIDS prevention programs that attempt to increase knowledge are needed by these youths, particularly for sexually delinquent youths.