We wished to identify the efficacy of enucleation (excavation) in the treatment of renal cell carcinoma. Surgical specimens from 26 patients with polar or peripheral lesions, 50 per cent of which were found incidentally by computerized tomography scan, were considered amenable to this form of treatment and were studied by ex situ enucleation after standard radical nephrectomy. Eleven patients were determined to have unsuccessful enucleation after histopathological study demonstrated capsular invasion, vascular invasion, residual tumor in the bed or multicentric tumors. Preoperative computerized tomography assessment did not accurately predict success of enucleation. The presence of a fibrous pseudocapsule of compressed renal parenchyma, which might facilitate a dissection plane and successful enucleation, did not correlate with tumor size. Microscopic examination of pseudocapsular integrity frequently revealed areas of thinning, disruption and penetration by neoplasm. When parenchymal preservation is necessary in the treatment of renal cell carcinoma, as wide a margin of adjacent renal parenchyma as possible should be excised with the tumor. In this study enucleation alone was associated with a significant risk of incomplete excision and, therefore, potential for treatment failure. We do not recommend enucleation in the presence of a normal contralateral kidney.