OBJECTIVE: To investigate the potential long-term effects of adolescent parenthood on completed education and income. DESIGN: Population-based birth cohort study. SETTING: All live births in 1982, whose mothers lived in the urban area of Pelotas, southern Brazil. SAMPLE: A total of 3701 participants: 1914 women and 1787 men at age 30 years. METHODS: Questionnaires were completed by the mothers in the early phases of this study, and by the cohort members in adolescence and adulthood. Linear regression models and G-computation were used in the analyses. MAIN OUTCOME MEASURES: Educational attainment and income at age 30 years. RESULTS: In women, adolescent parenthood was associated with lower attained education compared with women without adolescent maternity: by -2.8 years [95% confidence interval (CI) -3.2 to -2.3] if their first birth was at age 16-19, and by -4.4 years (-5.5 to -3.3) at age 11-15. These effects were greater among women who had three or more children. Women with adolescent parenthood also had 49 or 33% lower income at age 30 if their first child was born when aged 16-19 or 11-15, respectively. In men, the adverse effect of adolescent parenthood on education appeared to be mediated by a higher number of children and there was no effect of adolescent paternity on income at age 30 years. CONCLUSION: These findings suggest lasting socio-economic disadvantages of adolescent parenthood, with larger effects being apparent in women than in men. TWEETABLE ABSTRACT: Adolescent parenthood has an adverse effect on educational attainment later in life, and on household income among women.