Obese women (n = 104) were treated with an energy reduced diet (1100 kcal d-1) in a strictly standardized outpatient regime. Body composition, regional adipose tissue distribution, regional fat cell sizes and metabolic variables were followed before treatment, after 5% weight loss and at the stage when there was no further weight loss. Premenopausal women lost less body fat and relapsed earlier after treatment, compared with menopausal women. Fat loss appeared to be more uniform, and included several adipose tissue regions in postmenopausal women, while younger women seemed to lose fat mainly from the epigastrial fat cells. Higher baseline levels of thyroid hormones were associated with increased fat loss and a tendency to lose less lean body mass. Waist/hip and waist/thigh ratios did not change in response to weight loss. The addition of fibre to the diet did not affect the rate of relapse. These results suggest that obesity treatment by implementation of a negative calorie balance might be more successful in postmenopausal than in younger women, perhaps due to the more uniform availability of body fat in the former.