OBJECTIVE: Osteoporosis is associated with the pathogenesis and risk of urolithiasis, which is higher among postmenopausal women (as opposed to premenopausal). Bisphosphonates potently inhibit bone resorption, and are used in the management of bone disease. We investigated the ability of a bisphosphonate to prevent calcium stone formation. METHODS: We studied 12 postmenopausal women (63.8 +/- 7.3 years) who were not receiving osteoporosis therapy, and had stones comprised of calcium phosphate (CaP; n = 3), calcium oxalate (CaOx; n = 3) and CaP + CaOx (n = 6). We measured bone mineral density (BMD), serum and urinary values in 24-hour urine specimens before and 3 months after the oral administration of 5 mg/day of alendronate (ALN). The indexes of the ionic activity product of calcium oxalate, AP(CaOx), and of calcium phosphate, AP(CaP), were estimated using the Tiselius method. RESULTS: ALN significantly reduced the AP(CaP) index (1.53 +/- 1.37 to 0.89 +/- 0.81, p <0.05). Urinary calcium, oxalate, phosphate and the AP(CaOx) index did not significantly change. BMD improved in 11 of the 12 patients. Urinary stones did not develop in any of the patients during the course of the study. CONCLUSION: The results suggested that ALN not only improves BMD and osteoporosis, but also reduces the risk of calcium phosphate stone formation in postmenopausal women. Copyright (c) 2009 S. Karger AG, Basel.