Little is known about the effects of thyroid hormone excess in male patients. Our aim was to evaluate bone mineral density (BMD), bone turnover markers, and thyroid function in male patients with treated thyroid cancer on long-term suppressive L-T4 therapy (TC) and in male patients with Graves' disease (GD). We studied 49 male patients (aged 45+/-12 years), 17 with TC (29-288 months on L-T4 suppressive therapy; free T4: 1.9+/-0.6 ng/dl [normal< or =2.0]; TSH: 0.2+/-0.3 microU/ml [Normal 0.5-5.0]) and 32 with recent onset GD (<12 weeks, free T4: 2.0+/-1.4 ng/dl; TSH: 1.07+/-1.8 microU/ml; TSHRAb 53+/-45% [normal < 15]). BMD was measured by dual X-ray absorptiometry (DXA, Hologic QDR1000w) at the lumbar spine (L2-L4, LS), femoral neck (FN), and Ward's triangle (WT). Results were expressed as Z-score (SD compared to national controls). Total alkaline phosphatase (ALP), osteocalcin (BGP), iPTH, serum phosphorus, serum, and 24 h urine calcium were measured as bone markers. Age, weight, and body mass index were comparable in both groups. Patients with TC and with GD showed reduced axial BMD (95% confidence interval: LS: TC (-1.27-0.01)(P = 0.046), GD (-1.06 to-0.38)(P < 0.001); FN: TC (-0.82 to-0.16)(P = 0.007), GD (-0.95 to-0.15)(P = 0.008); WT: TC (-0.82 to -0.18)(P = 0.004), GD (-0.97 to -0.08)(P = 0.024). No significant differences in BMD were found between the groups. Among bone markers, total ALP and osteocalcin levels showed higher levels in Graves' disease (ALP: 139+/-76 vs. 88+/-34, P < 0.01; BGP: 7.5+/-3.7 vs. 4.6+/-1.6; P < 0.001). Our data suggest a mild deleterious effect of thyroid hormone excess in the axial bone mass from male subjects. A skeletal status assessed by BMD in male patients with chronic TSH suppression by L-T4 or history of hyperthyroidism is recommended.