Despite the widely described consequences of childhood and adolescent overweight and obesity the economics literature to date has almost exclusively focused on the relationship between body size and earnings among adults. We provide new evidence on the long-run labor market penalty of teenage overweight and obesity using unique and large-scale data on 150,000 male siblings from the Swedish military enlistment. Our empirical analysis provides four important results. First, we show for the first time that there is a large adult male labor market penalty for being overweight and obese as a teenager. Second, we show that this result can be replicated using data from the USA and the UK. Third, we show a strikingly strong within-family relationship between body size, on the one hand, and cognitive skills and non-cognitive skills, on the other hand. Fourth, we show that a large part of the estimated body size penalty reflects lower skill acquisition among overweight and obese teenagers. All of these results hint at the importance of policy combating early life obesity in order to reduce healthcare expenditures as well as poverty and inequalities later in life.