Several models of adolescent sexual activity have previously been published and most of them suggest two basic components, biological and sociological. This article highlights important environmental factors in shaping the sexual behaviour of the school-going youth in Uganda. Students in education levels Senior 1 to 6 participated in the study. Information was collected from self-response structured questionnaires, focus-group discussions, and discussions with teachers. Student respondents were randomly selected. The study found that 65 per cent of male and 32 per cent of the female unmarried secondary school students had sexual experience. Of the sexually active youth, 49 per cent of the males and 25 per cent of the females had multiple sexual partners. Four main environmental factors appear to be important in shaping school students’ sexual activity in Uganda today: parental care, peer influence, economic factors and AIDS education. Some elements accelerate and others suppress sexual activity.