High levels of thyroid hormones accelerate bone turnover. The aim of the present study was to evaluate the effects of treatment with alendronate in patients affected by hyperthyroidism and osteoporosis. We studied 40 hyperthyroid patients with bone loss, divided into two groups according to menopausal state. Before treatment and after 6 and 12 months, serum thyroid hormones levels, serum osteocalcin level and bone mineral density were evaluated. In all patients we observed an increase in bone mineral density after treatment with alendronate, and a corresponding decrease in serum osteocalcin level.