Bone histology and its relationship with calcium metabolism was evaluated in adult patients with nephrotic syndrome: 29 had normal renal function (GFR 103 ± 4 ml/min/1.73 m2) (group 1) and 20 had renal insufficiency (GFR 31 ± 4 ml/min/1.73 m2) (group 2). In group 1 serum PTH, 1.25-HCC and 24.25-HCC levels were normal, while 25-HCC values were reduced. Bone histology was normal in 76% of the patients, while 17% had isolated osteomalacia and 7% an associated bone resorption. Group 2 showed a higher incidence of bone resorption when compared with a matched group of patients with renal failure and no proteinuria (40% vs. 13%) and a comparable frequency of isolated mineralization defect (25% vs. 34%). PTH levels were definitely increased and serum total calcium and all the vitamin D metabolites were reduced. A significant correlation between the apparent duration of the disease and the severity of osteodystrophy was found only in group 2. In conclusion, no constant derangement of calcium metabolism and bone histology is evident in patients with nephrotic syndrome and normal renal function, while patients with persistent proteinuria are at high risk of osteodystrophy even in the early phases of renal failur