In this study, the effect of rapid and slow biological maturation on the development of obesity was investigated in boys (n = 79) and girls (n = 98), initially aged a mean of 13 y, and measured six times between 1977 and 1991. Obesity was determined by measuring body mass index (BMI; in kg/m2) and by summing four skinfold thicknesses. Biological maturation was operationalized by skeletal age, the age of peak height velocity (PHVage) for boys, and the age of menarche for girls. Multiple analyses of variance for repeated measurements showed that based on either skeletal age or PHVage, BMI for rapidly maturing boys was significantly higher than for slowly maturing boys between 13 and 27 y of age. Based on skeletal age, rapid maturers also showed higher mean sums of skinfold thicknesses over this period. For girls, BMI and sums of skinfold thicknesses for the rapidly maturing girls, based on either skeletal age or age at menarche, were also higher than for the slowly maturing girls over the entire period of study. In conclusion, individuals who matured rapidly in adolescence were, in general, more obese than slowly maturing adolescents between 13 and 27 y of age. Rapid maturation seems to have long-term consequences for obesity and should therefore be considered a risk indicator for the development of obesity.