The intention of the study was to know the family factors that are related with the beginning of sexual life of adolescents. A sample of 1942 students of Technical Schools in Mexico City (44.7% male and 55.3% female) was surveyed, of these 19.3% reported to be sexually active. In order to compare the other of the adolescents a equivalent sample was chosen in gender and age, to the sample of those who were sexually active. The sexually active females reported less communication and attachment with both parents and more rejection by the mother in comparison to those who were sexually in-active. Relative to the males, those that were sexually active, reported more communication on subjects of sexuality and more permissibity from both parents, as well as more rejection by the mother in comparison to males who reported sexually in-active.