To spare organ function, partial resection of early diagnosed renal-cell carcinoma (RCC) is applied for well-localized and small-volume RCC with increasing frequency, although recurrence of the tumor in the same kidney is occasionally observed. The aim of the present study was to establish objective prognostic parameters that would allow the selection of tumors suitable for an organsaving procedure. Of the 160 patients undergoing a radical nephrectomy, 67 were included in this study. In 7/45 patients with lymph-node dissection (15.6%), clinical staging revealed a false-negative lymph-node status. By means of conventional histopathology, multifocality could be demonstrated in 2/67 patients (3%); in 1/67 patients (1.5%), the ipsilateral adrenal gland was unexpectantly tumor-involved. Both tumor tissue and normal peritumoral tissue were examined for the presence of premalignant and tumor cells on the basis of DNA ploidy and of the expression of the tumor-associated G250 antigen, which is specifically expressed at the surface of renal cancer cells. In 40/67 (59.1%) peritumoral tissue specimens, cells with an abnormal DNA content could be observed using automated image analysis. In 12/67 cases (18%), cells obtained from peritumoral tissue also showed an aneuploid DNA histogram; 4/67 (6%) had a tumor-correlated DNA ploidy. Additionally, 38/67 (56.9%) of these tissues, histopathologically classified as normal, contained cells expressing the G250 antigen. These observations were independent of the stage or histological grade of the tumor. These data indicate that classic pathological parameters for tumor staging are insufficient for the detection of multifocality, occurring in more than 15% of cases. Additionally, it was shown that examination of tissue adjacent to the RCC allowed a specific detection of abnormal cells revealing abnormal ploidy or altered expression of tumor-associated antigens as compared with normal renal tissue in nearly 60% of cases investigated. The clinical relevance of this observation remains to be determined.