Computed tomography (CT) was carried out in 31 patients 10-43 years after surgery for renal cell carcinoma, 10 belonging to a consecutive series of patients operated upon at one urological department 10 years previously. Twenty-eight patients were symptomless, and 3 had flank pain, severe fatigue and hematuria, respectively. Cancers in the remaining kidney were found 13-21 years after nephrectomy in 4 of 31 patients (12.9%). The 3 patients with symptoms were among these 4. An adenoma was found in 1 patient 10 years after nephrectomy. The cancers were treated by renal resection in 2 patients, multiple tumors made nephrectomy necessary in 1 patient and 1 patient was not operated upon because of disseminated disease. The adenoma indicated future checkup by CT. Three of the 4 new cancers had a dismal outcome. The renal parenchyma was found to be essentially normal in all the other 26 patients, irrespective of the widely varying time interval between nephrectomy and CT. Asynchronous bilateral renal cell carcinoma has a poor outcome which presumably can be improved by early diagnosis and aggressive treatment. CT is the method of choice for early detection and follow-up of renal tumors. It should be carried out every other year after nephrectomy for renal cell carcinoma.