We studied the pathologic features and whether clinical features could predict pathologic outcomes in small renal masses. The study included all adult patients with solitary, nonmetastatic renal masses 4 cm or smaller confirmed by nephrectomy or needle biopsy between 2004 and 2006. Tumor size, histologic type, Fuhrman nuclear grade, and stage were obtained from surgical pathology reports. Clinical variables included age, sex, tumor size, and symptomatology. The study included 290 men and 198 women (mean age, 59.3 years). Median tumor size was 2.6 cm (range, 0.5-4.0 cm). Approximately 84% of masses were incidentally detected. Nonneoplastic entities, benign neoplasms, and low- and high-grade carcinoma accounted for 1.6%, 18.0%, 49.0%, and 31.4% of masses, respectively. Women were more likely to have a benign mass (27.3% vs 14.5% of men, P < .001). Age (P = .56), tumor size (mean, 2.63 vs 2.46 cm for benign; P = .08), and symptomatology (P = .46) were not associated with malignancy. Multivariate analyses using sex, age, tumor size, and symptomatology failed to produce a model useful to predict the pathology of individual tumors. This inability may argue for an increased role for needle biopsy in their evaluation. © American Society for Clinical Pathology.