In the population of 242,633 draftees examined in the Copenhagen area for the period 1956–77, 1143 were extremely overweight. Compared to 2123 controls, selected at random from the remaining draftee population, the obese had a lower educational attainment, even at each level of intelligence test score. Conversely, at each educational level, the obese did not differ from the controls in intelligence test score. When taking into account, by regression analysis, both intelligence test score and parental social class, the chance for the obese of exceeding the educational level of minimum years of schooling followed by elementary trade training increased from 37% to only 52% of that for the controls. The results suggest that obesity, irrespective of social origin, is associated with poor educational attainment which may be responsible for the cognitive deficiency manifested in lower intelligence test scores.