In order to study the presence of possible renal damage, 12 patients who had been chronically treated with 1,25-dihydroxycholecalciferol therapy, 1,25(OH)2D3, for hypoparathyroidism, pseudohypoparathyroidism, and hypophosphatemic rickets were examined by renal ultrasound. Two patients had normal values while 10 subjects showed nephrocalcinosis (NC) of mild, medium, or severe degree. The echographic results have been related to some calcium-phosphorus metabolism and therapeutic parameters. In those subjects with medium to severe NC, the age at the beginning of therapy was significantly younger and the dose of 1,25(OH)2D3 was significantly higher, than in the other patients. Laboratory data were not predictive of NC. Renal ultrasound is, therefore, a useful means of screening to detect even early stages of NC; its use in the follow-up is also recommended.