In this study we evaluated the relationship between serum active vitamin D levels and severity of osteoporosis in patients with postmenopausal osteoporosis and we examined the effect of vitamin D levels on the efficacy of the treatment. Twenty osteopenic patients were followed for 6-8 months as control group. Eighty patients with postmenopausal osteoporosis have randomly taken tibolone, calcitonin, calcitriol or etidronate for 6-8 months, 20 in each group. Demographic characteristics, age of menopause, daily calcium intake, history of fracture of the patients were inquired by a protocol. Bone mineral density (BMD) by DEXA, serum 1,25 (OH)2 vitamin D, parahormone (PTH) and estrogen levels, urinary hydroxyproline and calcium levels were measured at the beginning of the study and repeated after 6-8 months follow-up period. No correlation was observed between levels and serum 1,25 (OH)2 vitamin D and BMD, duration of menopause or history of fracture. Laboratory parameters such as serum PTH and estradiol levels and urinary hydroxyproline and calcium were also not correlated with serum 1,25 (OH)2 vitamin D levels. Serum 1,25 (OH)2 vitamin D levels were in normal range in patients and controls. After 6-8 months treatment the efficacy of treatment by BMD and urinary hydroxyproline levels were found to be independent from serum 1,25 (OH)2 vitamin D levels. We conclude that serum 1,25 (OH)2 vitamin D levels don't play a major role on the severity of postmenopausal osteoporosis and the efficacy of osteoporosis treatment. The role of vitamin D in postmenopausal osteoporosis should be examined at receptor level.