Renal oncocytoma: long-term follow-up and flow cytometric DNA analysis. We report a retrospective study on the clinicopathologic features and flow cytometric DNA analysis of ten renal oncocytomas compared with a control group of ten randomly selected renal cell carcinomas. Among the oncocytoma patients, no recurrences or metastases were noted over an average follow-up of 6.7 years (range = 6 months to 16 years). Reproducible, high-quality DNA histograms were obtained on the paraffin-embedded specimens by using our modified flow cytometric procedure. One aneuploid (10%) and two hyperdiploid tumors (20%) were found in the oncocytoma group. There was no correlation between these abnormal DNA histographic patterns and survival or tumor stages. On the contrary, a good correlation was found between tumor grades and DNA ploidy in the controls. We conclude that renal oncocytoma is a clinically benign tumor, yet it may exhibit varying degrees of flow cytometric DNA abnormalities, which have no predictive value on survival and probably reflect the characteristics of oncocytes rather than its malignant potential. 