The aim of this study was to determine the correlation between histological subtype, size, grade, and stage of the kidney tumors and to investigate whether a correlation exists between the size of the kidney tumor and its behavior.Between 1996 and 2004, we had 212 patients with radical or partial nephrectomy due to a kidney tumor at Shaheed Labbafinejad Medical Center. Their pathologic blocks were re-evaluated with consideration of their tumor size and pathologic features.Of 212 pathologic blocks, 17 (8%) were benign and 195 (92%) were malignant masses including 179 renal cell carcinoma (RCC) tumors. Malignant tumors were slightly greater compared with the benign ones (P=.10). There was no significant relation between the size of tumor and the histological subtype. Significant relations between the size of the kidney tumor and the nuclear grade (P=.007), clinical symptoms (P=.02), and extracapsular extension (P<.001) were observed. In smaller RCC tumors (< 4 cm), extracapsular extension (stages T3 and T4) was rare (1 in 29). However, smaller RCC tumors were not significantly different from those larger than 4 cm regarding the nuclear grade, symptoms, and histological subtypes.Tumor size is not an independent predictor for the histological subtype of the tumors; however, larger malignant tumors may have higher grades, higher stages, and clinical symptoms.