Because treatment with thyroid hormone has been reported to reduce bone mineral density, health care providers and patients alike have become confused and alarmed in regard to risks of osteoporosis and potential bone fracture. In this review, the available data bearing on this issue are briefly described and a rational approach to management is proposed. When considering thyroid hormone treatment, the clinician must weigh the indications for such therapy against possible adverse effects on bone mineral, and be cognizant of the distinction between replacement and suppressive therapy, since there is accumulating evidence to indicate that even mild degrees of chronic excess of thyroid hormone therapy may accelerate the natural course of osteoporosis. Current and future experimental protocols in patients tak-potential benefit of adjunctive agents that inhibit bone resorption such as calcitonin or organic biphosphonates. For the time being, however, enlightened use of the new highly sensitive thyrotropin assays will allow the physician to lower the risk of osteopenia in patients taking thyroid hormone.