Previous investigations have suggested that a lower-than-normal serum 1,25(OH)2D is found in elderly women with postmenopausal osteoporosis. We examined the fundamental aspects of this theory by investigating serum vitamin D metabolites in four representative samples of Caucasian women. These included 44 early postmenopausal women divided into two subgroups: fast bone losers, that is, bone loss greater than 3%/year (n = 20), and "physiological" bone loss (n = 24); and 28 70-year-old women divided into two subgroups: with and without osteoporotic fractures. Serum 1,25(OH)2D concentrations were virtually the same in all groups thus contradicting the previous reports of low 1,25(OH)2D in elderly women. Furthermore, mean 25OHD and 24,25(OH)2D did not differ between the groups. We conclude that 1,25(OH)2D is unlikely to be significant in the development or treatment of a majority of women with postmenopausal osteoporosis.