SUMMARYThe paper intended to find the prevalence of HIV infection risk-related behaviours among third year senior secondary school students in Port Harcourt metropolis. A cross-sectional survey among 1800 third year senior secondary school students randomly selected from thirteen secondary schools in Port Harcourt metropolis was done using two-stage sampling technique. Demographic data and information on the sexual behaviour of each student in the study group was obtained from self-administered structured questionnaire. The prevalence of sexual intercourse was 61.1%. Males were more sexually active than females. Age of first sexual intercourse was 13.2±5.6 years for males and 13.9±4.1 years for females. Of the sexually active students, 32.6% had multiple sexual partners. Sexual activity of the students did not increase with age. The prevalence of Intravenous drug use (IVDU) was found to be 1.4%. The use of intravenous drugs was more among the males (80.8%) than among the females. The prevalence of blood transfusion is 10.3%. Among the sexually active students only 437 (36.9%) used condom. Sex of student, social class and school gender were significant predictors of ever-had sexual activity. The paper concludes that the prevalence of sexual behaviour related to the development of HIV/AIDS amongst the students is high. The need to highlight HIV/AIDS education programmes in the school curriculum of adolescents is discussed. [Afr J Health Sci. 2008; 15:42-49]