Preoperative axial computerized tomography scans in 163 patients with renal cell carcinoma were reviewed to assess the predictive value for the diagnosis of regional lymph node metastases. Computerized tomography was falsely negative in 5 patients: 2 had metastatic lymph nodes in the renal hilus adjacent to the primary tumor measuring 2 and 2.5 cm., and 3 had micrometastases in nodes of less than 1 cm. In 43 patients enlarged lymph nodes with a diameter of 1 to 2.2 cm. (median 1.4 cm.) were diagnosed on the preoperative scan and this was confirmed at nephrectomy and pathologically. In 18 of these 43 patients (42%) histological study showed metastases of the renal cell carcinoma in the enlarged lymph nodes. In the other 25 patients (58%) the enlarged nodes showed only inflammatory changes and/or follicular hyperplasia. This finding was significantly more frequent in patients with tumor involvement of the renal vein and tumor necrosis (p = 0.0044). We conclude that the sensitivity of preoperative computerized tomography is good for the detection of enlarged lymph nodes in patients with renal cell cancer (95%). However, significant lymph node enlargement frequently may be caused by inflammatory changes, especially in the presence of tumor necrosis. This radiological finding should not be misinterpreted as metastatic disease, unless it has been proved cytologically by fine needle aspiration.