Transitional cell carcinoma of the renal pelvis presenting as a renal abscess.

We report on a 76-year-old woman who was diagnosed with a primary renal abscess of the left kidney. After percutaneous drainage, no clinical improvement was observed. Surgical exploration and nephrectomy were performed. The histologic evaluation revealed an unsuspected transitional cell carcinoma of the renal pelvis, which had been misinterpreted as a primary renal abscess. Malignancy must be considered as an underlying cause for the formation of a renal abscess, especially if no other predisposing factors such as diabetes mellitus or urinary stones are present.