Per- and polyfluoroalkyl substances (PFAS) exposure may increase adiposity and obesity risk in children. However, no studies have extended these findings into adolescence or identified periods of heightened susceptibility. We estimated associations of repeated pre- and postnatal serum PFAS concentrations with adolescent adiposity and risk of overweight/obesity. We studied 212 mother-offspring pairs from the HOME Study. We quantified serum concentrations of four PFAS in mothers at ∼16 week gestation and their children at birth and ages 3, 8, and 12 years. We assessed adiposity at 12 years using anthropometry and dual-energy X-ray absorptiometry. Using multiple informant models, we estimated covariate-adjusted associations of an interquartile range (IQR) increase in log2-transformed PFAS for each time period with adiposity measures and tested differences in these associations. Serum perfluorooctanoate (PFOA) and perfluorohexane sulfonate (PFHxS) concentrations during pregnancy were associated with modest increases in central adiposity and risk of overweight/obesity, but there was no consistent pattern for postnatal concentrations. We observed nonlinear associations between PFOA in pregnancy and some measures of adiposity. Overall, we observed a pattern of modest positive associations of gestational PFOA and PFHxS concentrations with central adiposity and the risk of obesity in adolescents, while no pattern was observed for postnatal PFAS concentrations.