The aim of this randomized, controlled study was to evalaute effects of 12 months alendronate therapy on bone mineral density (BMD) and markers of bone formation and resorption in women with postmenopausal osteoporosis. Study enrolled women with BMD at least 2 SD below adult, premenopausal BMD mean. Patients to be treated were randomized into two groups. Patients in the control group received 500 mg elemental calcium tablet daily and treatment group received 10 mg/day alendronate and 500 mg elemental calcium tablet for twelve months. Pretreatment characteristics of patients in both groups were similar. A significant increase in BMD of the treatment group patients compared to control group was observed at 12 months (p < 0.001). Markers of bone formation and resorption in the treatment group reduced significantly at 6 and 12 months of therapy compared to control group (p < 0.001).