Exposure to chronic glucocorticoid (GC) excess determines changes in body composition. The aim of the study was to compare body composition in women exposed to endogenous hypercortisolism (Cushing's syndrome, CS), exogenous glucocorticoid treatment (rheumatoid arthritis, RA) and controls. Fifty-one CS women, 26 RA women treated with low-dose prednisone (5 mg/day or 10 mg/2 days), and 78 female controls were included. Fourteen CS patients were hypercortisolemic, 37 in remission (10 required hydrocortisone substitution after surgery). Body composition parameters were measured by dual-energy X-ray absorptiometry scanning (DEXA). RA patients had a greater waist-hip ratio (WHR) (p<0.01), less lean body mass (LBM) (p<0.01), and lumbar bone mineral density (BMD) (p<0.01) than controls. CS patients, globally and those with cured disease, had more total fat (both percentage and kg) and trunk fat percentage, and less whole body-BMD than RA patients (p<0.05, p<0.01, p<0.05, respectively). Active CS patients had less whole body-BMD and more LBM than RA patients (p<0.05, p=0.01, respectively). Cured CS patients not taking hydrocortisone had more total fat [both percentage (p<0.05) and kg (p<0.05)], trunk fat percentage (p<0.05), lumbar BMD (p<0.01) than RA patients. Cured CS patients requiring hydrocortisone only differed from RA patients by smaller WHR (p<0.01). All the differences in BMD disappeared when the data were reanalyzed including only the estrogen-deficient groups. Hypercortisoliof CS determines an irreversible increase in body fat, greater than in RA. Endogenous and exogenous exposure to GC negatively affects body composition by increasing the WHR. There appears to be no additional effect on BMD in estrogen-deficient women.