OBJECTIVE We reviewed the records of patients submitted to renal transplantation at our institution to determine the incidence and risk factors for calculus formation in these patients. METHODS Of 794 functioning renal grafts that had been transplanted from January, 1981 to May, 1996, 16 patients (2%), 9 males and 7 females, had upper urinary tract calculi post-transplantation. All 16 patients had received kidneys from cadaver donors. Three had donor graft lithiasis. The calculi were located predominantly in the calyces, at multiple sites in 7 patients and the mean size was 8.3 mm. The composition of the calculi was predominantly uric acid. Four patients who developed sudden obstructive anuria with elevated serum creatinine, underwent percutaneous drainage. RESULTS All patients had one or more stone-predisposing factors, such as obstructive uropathy, recurrent urinary tract infection or metabolic abnormalities (predominantly hyperuricosuria). Five patients passed their stones spontaneously, 7 patients with uric acid stones were treated with urinary alkalinization, two patients underwent open pyelolithotomy, one underwent percutaneous nephrolithotomy and one patient with a small asymptomatic caliceal stone was managed conservatively (watchful waiting). During long-term follow-up (mean 69 months), 4 patients lost the real graft [only one case was related to urinary calculi (primary hyperoxaluria)] and 4 patients had recurrent calculi. CONCLUSIONS Urinary lithiasis after renal transplantation is a relatively uncommon complication. A multifactorial etiology for calculus formation has been observed. The predisposing factors and composition of the calculi, but not frequency, are identical to those of non-transplant patients. A variety of methods are used to treat posttransplant calculi. The least invasive treatment available should be utilized according to the likelihood of recurrence and the need to preserve renal function. With adequate treatment and prophylaxis, posttransplant urolithiasis does not appear to affect graft function.