The aim of the work was the estimation of the ionized magnesium level in postmenopausal osteoporotic women in different stage of osteoporosis progression assessed in densitometrical investigation. The study included 53 women, divided due to T index into 3 subgroups compatible with WHO osteoporosis classification criteria. The control group included 20 healthy women at perimenopausal age. In the group of women with osteoporosis and severe osteoporosis significantly lower ionized magnesium level was determined in comparison with the control group and the group of women with osteopenia (p < 0.05). No correlation between T index (assessing the stage of osteoporosis progression) and hypomagnesaemia was found.