We evaluated the pathogenic role of Corynebacterium urealyticum in the development of encrusted pyelitis (EP) and encrusted cystitis (EC), and their clinical consequences in renal transplant recipients. During a 4-year period, we studied seven renal transplant recipients with EP and two with EC. The records of 320 other renal transplant patients studied during the same period were used as a control group. C urealyticum (> or = 10(5) CFU/ml) was isolated from 4 patients with EP (urine 3, blood 1) and from 1 patient with EC (urine). Alkaline urines with struvite crystals, microscopic hematuria, and sterile conventional urine cultures were present in all our cases. All the patients with EP developed obstructive uropathy with deterioration of the renal function and pyelonephritis (4 patients) or renal abscesses (3 patients). Chronic urinary discomfort and macroscopic hematuria were present in the 2 patients with EC. Long-term vesical and ureteral catheterization were considered the most important risk factors for the development of EC and EP, respectively. Vancomycin was successfully used in 5 cases, but all the patients required a derivative procedure or a surgical resection of the incrustations to improve. We conclude that EP and EC should be investigated in renal transplant patients who develop pyelonephritis, obstructive uropathy, or chronic urinary symptoms. EP and EC could lead to the loss of their grafts. C urealyticum appears to have a pathogenic role in these entities.