Our purpose in this study was to determine the prevalence of undetected disorders of bone and mineral metabolism in women with osteoporosis and to identify the most useful and cost-efficient screening tests to detect these disorders. A cross-sectional study was conducted among 664 postmenopausal women with osteoporosis at the Osteoporosis and Metabolic Bone Disease Program at the Mount Sinai Hospital in New York between January 1992 and June 1996. Women without a history of diseases or medications known to adversely affect bone who completed extensive laboratory testing including complete blood count, chemistry profile, 24-h urinary calcium, 25(OH)vitamin D, and PTH were included. Among 173 women who met the inclusion criteria for the study, previously undiagnosed disorders of bone and mineral metabolism were identified in 55 women (32%). Disorders of calcium metabolism and hyperparathyroidism were the most frequent diagnoses. A testing strategy involving measurement of 24-h urine calcium, serum calcium, and serum PTH for all women and serum TSH among women on thyroid replacement therapy would have been sufficient to diagnose 47 of these 55 women (85%) at an estimated cost of $75 per patient screened. Previously undiagnosed disorders affecting the skeleton are common in otherwise healthy women with low bone density. A simple testing strategy is likely to identify most such disorders.