Determinants of sexual activity and intentions for condom use were examined guided by the Attitude, Social influences, and Self-efficacy (ASE) model as a theoretical framework. A total of 561 in and out-of-school youth (15-24 years) in Addis Ababa completed a self-administered questionnaire. A third of them reported sexual intercourse in the past and half of the sexually active used condoms during recent intercourse. Being out-of-school, male, aged 20-24 years, alcohol use and khat (amphetamine-like substance) consumption predicted the likelihood of engagement in sexual activity. Of these variables, however, male sex was more associated with reported condom use during recent sexual intercourse. Self-efficacy, skills, and barriers predicted 23% of the variance in intentions to use condoms. Self-efficacy was also associated with past condom use. Psychosocial constructs predicted more variations in condom use intention for males than for females. In general, self-efficacy was found to be the strongest predictor of the constructs, whereas attitude and social influences were the weakest. The study implies that HIV/AIDS prevention programmes for young people in Ethiopia need to emphasize building assertive communication skills in sexual negotiations and condom use. Minimizing the gender gap in sexual relationships forms the cornerstone for such educational strategies.