Optimal sleep quality fosters adolescents' wellbeing and, therefore, learning about its developmental determinants is essential. We examined how early family environment (i.e., parent-reported parenting, marital relationship quality, and mothers' mental health), obstetric factors (i.e., infertility history and assisted reproductive treatments, and pre- and perinatal complications and health risks), and children's emotion regulation in middle childhood predicted adolescents' sleep quality. We also tested the mediating role of emotion regulation in linking early determinants to adolescent sleep. Finnish families (N = 984) participated during pregnancy, infancy, middle childhood, and late adolescence. Results showed that only early maternal mental health problems predicted poor adolescent sleep quality. Contrary to hypotheses, emotion regulation did not mediate the effects of early family environment and obstetric factors on later sleep quality. Supporting the early family environment through improving maternal mental health can have long-term positive developmental impacts, including sleep.