Abstract: Background: The issue of early onset of fertile life among adolescent girls remains very current. However, theoretical predictions predict event decline, particularly with the young generations. This study aims to analyse trends and explanatory factors of early onset of fertile life among adolescent girls aged 15 to 19 years in Benin. Data and methods: The study uses Demographic and Health Surveys (DHS). The Kaplan Meier method and the Cox proportional risk model were used. Findings: Early onset of fertile life has experienced saw tooth variations between 1996 and 2017. The main risk factors are: education level, age at first sexual intercourse, and socio-economic standard of living. Conclusion: Interventions need to be strengthened and/or reoriented to effectively contribute to reducing the incidence of early onset of fertile life. This will enhance adolescent girls l‹nowledge and skills enabling them to live a healthy, responsible and timely sexual and reproductive life. Keywords: Fertility, adolescent girls, Benin.