This study aimed at identifying the associated aspects with the sexual initiation among adolescents from the east area of São Paulo City, Brazil. A quantitative cross-sectional study was conducted in 2007 with 385 15 to 19 year-old adolescents. The analyses were carried out in SPSS 15.0 separated into men and women. They were 16.8 years-old on average (standard deviation = 1.3) and 70.9% were students whereas only 25.9% were workers. Age and study status were associated to the onset of sexual life, both for men and women. Many other aspects, such as family norms and peer behavior were also found to be associated in different ways, to the sexual initiation. Results point out important contexts that seem to have a strong influence in the sexual initiation, and it should be emphasized that these aspects are present in any adolescent routine life.