A retrospective analysis of osteoporotic patient records was conducted to evaluate the effect of supplemental calcium (Ca) on urinary and serum Ca. Forty-seven patients composed the Ca-supplemented group and 17 patients the nonsupplemented group. Serum Ca values (mean±SD) were 9.3±0.3 and 9.4±0.4 mg/dl in the nonsupplemented and supplemented groups, respectively. Daily urinary Ca was 137±88 and 162±89 mg, respectively. Each group had similar concentrations of serum phosphorus, albumin and creatinine. Data from the Ca-supplemented group were divided into low and high Ca intake. In the low intake group (1000 mg/day), the values were 9.5±0.5 and 160±90, respectively. Seventeen and 36% of nonsupplemented and supplemented patients used estrogen, respectively. No significant effects of estrogen therapy were observed on serum or urinary Ca in either group. More detailed analysis of five patients was undertaken to evaluate the combined effect of supplemental vitamin D (ergocalciferol or calcitriol) and Ca on urinary Ca output. Baseline urinary Ca was 33±19 mg with an average daily Ca supplement of 1160 mg. After 4–8 weeks of supplementation with Ca and vitamin D, urinary Ca increased to only 68±33 mg. We conclude that supplemental Ca does not appear to cause a significant increase in urinary Ca and that added vitamin D has little effect on elevating urinary Ca in some older women. At the clinical level, use of Ca supplements will probably not lead to increased prevalence of hypercalciuria or nephrolithiasis; however, large variations among patients must be considered in the clinical use of Ca supplements.