This paper uses survival methods to assess the relationship between perceived peer behavior and the timing of first sex among Rwandan youth. The data derive from a 2001 survey among youth aged 15-24 years in four provinces: Kigali Ville, Butare, Kibuye, and Umutara. A total of 1327 male and female youth were interviewed through a structured questionnaire that includes questions on sexual attitudes and behaviors. The findings showed that the perception that peers are sexually active is associated with increased likelihood of experiencing early sexual debut. For both sexes, the relationship between perceived peer behavior and the timing of first sex is stronger in young adulthood than in late adolescence. Among female youth, the presence of the father appears to weaken the role of perceived peer behavior. A similar tendency is not found for male youth.KEY WORDS: youth; sexual debut; Rwanda; peer behavior.