The surgical technique, course and complications were analysed in 123 patients in whom a kidney tumor had been enucleated. Fifty-seven enucleated tumors were available for image analysis DNA-cytometry. In 49 patients there was an imperative indication for an organ-preserving operation, because nephrectomy would have made dialysis obligatory. In 74 patients with a healthy contralateral kidney the tumor was enucleated by choice. Thirty-five of 49 patients with an imperative indication are without sign of tumor progression after a mean follow-up of 4.5 years. In two patients there was a recurrence after 4 and 5 years, respectively, requiring a second organ-preserving operation. In one further patient there is a suspicion of multiple small tumor lesions 2 years after the first operation. Known metastases were present in 3 of 6 patients who died of their tumors. Sixty-eight of 74 patients operated on electively are without signs of tumor progression after a mean follow-up period of 3.3 years. One patient died from tumor metastases. Two patients had tumor recurrence, requiring nephrectomy and enucleation, respectively.