To determine bone mineral density in patients with differentiated thyroid carcinoma receiving thyroxine replacement therapy in suppressive doses, we studied 65 patients (47 women and 18 men; age 25-83 years, mean+/-SD 52.5+/-15.4 years). Patients were free of thyroid cancer in clinical and laboratory examinations at the time of the study. Bone mineral density of the lumbar spine and both hips was measured by dual-energy X-ray absorptiometry. There was no decrease in bone density in either 32 postmenopausal or 15 premenopausal women compared with an age- and sex-matched control group, nor was any decrease in bone density found in men. Our data suggest that thyroxine treatment in suppressive doses in patients with differentiated thyroid carcinoma is not a risk factor for the development of osteoporosis.