OBJECTIVE: Owing to the housing crisis in Cairo, many Egyptian families whose houses were ruined, and cannot afford new ones, are obliged to live in cemetery courtyards. The aim of this research is to evaluate sexual behaviour and HIV prevalence among the overcrowding inhabitants of cemeteries in greater Cairo. METHODS: The Arab International Center for Fighting Against AIDS made a research on 930 of adolescents and young adult inhabitants of cemeteries (630 males & 300 females) to assess their sexual behaviour and HIV prevalence among 150 persons. RESULTS: The following results were found: 1-42.5% of girls (128 girls) were sexually active by age 14. 2-71% of boys (448 boys) were active by age 16. 3-First sexual experiences were characterised by pain, guilt, and both bad and pleasing feelings, which influenced later sexual experiences. 4-The immediate reason for becoming sexually active at an early age is being used to listen to parents' voices while practicing sexual intercourse in the same place. 5-Other factors are low social status, poverty, ignorance, rape, lack of parental supervision, peer pressure, etc. 6-The no of HIV. + ve cases by ELISA test was 8 persons (5% nearly). DISCUSSION & CONCLUSIONS: Since the major, original reason for early sexual activity among young inhabitants of cemeteries in Cairo is overcrowding due to housing crisis. It is essential to provide economic sanitary houses for the poor overpopulated families and improve their socio-economic status. It is essential as well to give more attention to family planning (e.g. by providing condoms). Sex and HIV educational programs must be planned. Communication, media have a major role in this respect.