OBJECTIVES: To evaluate the efficacy of alendronate for premenopausal women with low bone density not resulted from secondary causes. MATERIALS AND METHODS: Forty thee women who was diagnosed low bone mineral density (BMD) before menopause were included. All patients were evaluated by history taking, physical examination, and laboratory investigation to rule out underlying secondary causes of osteoporosis. They were randomized into two groups: Group I was administered oral alendronate 70 mg per week and Group II was not. All the participants received calcium carbonate 1,250 mg and cholecalciferol 1,000 IU daily. Bone mineral density by dual energy X-ray absorptiometry was measured before and after 1 year of treatment. RESULTS: At baseline, there were no significant differences among the two groups in patient's age, body mass index (BMI), and BMD. After 1 year of treatment, Group I showed significant increase in BMD. CONCLUSIONS: In premenopausal women with low BMD in the absence of secondary causes for osteoporosis, alendronate treatment for 1 year may increase BMD. We suggest that management of low bone density in the premenopausal women without secondary causes should be considered.