We report the case of a 71-year-old male who presented with squamous cell carcinoma of the renal pelvis in a solitary functioning kidney, 34 years after orchidectomy and adjuvant retroperitoneal radiotherapy for stage II seminoma. This rare second malignancy occurred in the radiation treatment field. Second malignancies are an uncommon but serious sequela of radiotherapy, with potential for significant health problems in patients with complete remission of primary disease. To our knowledge, this is the first report of squamous cell carcinoma of the renal pelvis occurring after radiation treatment.