Renal masses secondary to metastases are not common. Few comprehensive reviews exist, which consist primarily of autopsy and radiologic reports. The purpose of this study was to review the types and incidences of various neoplasms which metastasize to the kidney and to determine the usefulness of fine-needle aspiration (FNA) in diagnosing them. Two hundred and sixty-one radiologically guided FNAs of renal lesions over a 9-yr period were reviewed. The diagnoses of the 261 renal FNAs were as follows: 136 (52%) were malignant, 111 (43%) were benign, and 14 (5%) were unsatisfactory. Of the 136 positive FNAs, 28 (21%) revealed metastatic tumors. The overall incidence of renal FNAs displaying metastatic tumors was 11%. Among the 28 patients with metastases to the kidney, 23 patients were men and 5 were women, with the mean age being 58 yr. Twenty-five patients (89%) had prior history of a primary malignancy, including lung carcinoma (11 cases, 39%), lymphoma (8 cases, 29%), hepatocellular carcinoma (3 cases, 11%), and one case each of breast, pancreatic, and cervical cancer. In the remaining 3 patients (11%), with metastatic adenocarcinoma (2 cases) and squamous-cell carcinoma (1 case), the primary tumor site remained unknown despite an extensive clinical workup. Overall survival after FNA was poor, with a mean of 9.8 mo. FNA is useful in the diagnosis of masses in the kidney secondary to metastatic disease. This information is of clinical importance, principally in the exclusion of a primary malignancy, but also to avoid unnecessary surgery and to plan for subsequent patient care.