65 women whose build ranged from normal to grossly obese were investigated to test the hypothesis that obese people, especially those with a genetic predisposition to obesity (manifest by early onset and family history of obesity), have a low energy expenditure. For the group as a whole, resting metabolic rate was related to obesity index, but the age of onset and family history of obesity had no effect on this relationship. The findings suggest that a familial predisposition to obesity is more likely to relate to energy intake than to energy expenditure.