OBJECTIVE The presentation of sarcoidosis with renal stones has never been evaluated in a prospective study. METHODS We have studied 110 consecutive patients with histologically proven sarcoidosis, first seen in the years 1993-1994 in the Milan Sarcoid Clinic. Those who had renal stones preceding or suggesting the diagnosis of sarcoidosis, and those who had evidence of renal calculi at presentation, were studied up to 31 December 1995 with serial evaluation of calcaemia, calciuria and serum 1,25 (OH)2D3 and are the basis of this report. RESULTS Four patients had had calculi a long time ago and probably unrelated to their sarcoidosis. Three patients had a previous history of recurrent colic with calculi. In one further patient the occurrence of calculi suggested the diagnosis. In three other patients pyuria or microscopic haematuria at the presentation of pulmonary sarcoidosis led to the diagnosis of asymptomatic calculi. All the above seven patients had features of chronic disease and required long term corticosteroid therapy. Four of them required lithotripsy or pyelotomy before starting steroid therapy. Another had further calculi during the follow-up, and an episode of hydronephrosis requiring lithotripsy, due to poor compliance to corticosteroid therapy. Another patient had a single stone during follow-up in spite of proper therapy. In all the others prednisone was useful to control the disease. Summing up the results of a previous similar but retrospective study from our clinic, we can describe the full spectrum of nephrolithiasis at presentation of sarcoidosis, as it appears from the examination of 729 consecutive patients seen over 17 years (1978-1994), with a further follow-up of at least one year (see Conclusions). CONCLUSIONS 1. Renal stones may be the presentation of sarcoidosis in 3.6% of cases, but the etiology may go unrecognized for many years in most of them. 2. There are asymptomatic renal stones at presentation in a further 2.7%: pyuria or microscopic haematuria may suggest such an occurrence. 3. Renal calculi appear to be a marker of chronicity, with long term corticosteroid therapy required in most cases. 4. A diagnosis of sarcoidosis should always be considered when patients present with renal calculi of unknown origin.