We study the effect of birth weight on long-run outcomes using data on Swedish twins born between 1926 and 1958 linked to administrative records spanning entire life-time labor market histories. We find that birth weight positively affects permanent income and income across large parts of the lifecycle. The timing of the birth weight–income relationship is in line with the role of birth weight in determining takeup of sickness benefits and morbidity. The effect of birth weight on labor market outcomes even for cohorts born 30 years apart are similar; for short run health outcomes, birth weight plays a decreasing role over time.