In a sample of over one million Swedish first-born offspring, we examined associations between early maternal age at first childbirth (MAFC; i.e., < 20 and 20-24 vs 25-29 years) and offspring non-accidental deaths, accidental deaths, deaths by suicide, non-fatal accidents, and suicide attempts. We included year of birth and several maternal and paternal characteristics as covariates and conducted maternal cousin comparisons to adjust for unmeasured confounding. Early MAFC (e.g., teenage childbearing) was associated with all outcomes, with the most pronounced risk elevation for accidental deaths [Hazard Ratio (HR) < 20 2.50, 95% confidence interval (CI) 2.23, 2.80], suicides (HR < 20 2.08, 95% CI 1.79, 2.41), and suicide attempts (HR < 20 2.85, 95% CI 2.71, 3.00). Adjusting for covariates and comparing cousins greatly attenuated associations (e.g., accidental deaths HR < 20 1.61, 95% CI 1.22, 2.11; suicides HR < 20 1.01, 95% CI 0.69, 1.47; and suicide attempts HR < 20 1.35, 95% CI 1.19, 1.52). A similar pattern emerged for non-accidental deaths and non-fatal accidents. Therefore, results indicated maternal background factors may be largely responsible for observed associations.