Immunohistochemical study and flow cytometric DNA analysis were done on seven cases of clear cell sarcoma of the kidney (CCSK) to speculate its histogenesis and to access the diagnostic usefulness of these methods in the differential diagnosis of Wilm's tumor. Clinically, CCSK is a rare malignant renal tumor of children with a propensity to metastasize to bone. Arborizing vascular pattern surrounding the tumor cells which have clear cytoplasm is characteristic histologic finding. Immunohistochemically, only vimentin was diffusely demonstrated in the tumor cell membrane and cytoplasm. In flow cytometric DNA analysis, four cases showed diploidy and two cases near diploidy. CCSK is a separate disease entity with characteristic clinicopathologic, immunohistochemical and flow cytometric findings in distinction from Wilms' tumor. Considering the histologic and immunohistochemical findings, the possible histogenetic mechanism of CCSK seems to be in common with congenital mesoblastic nephroma (CMN), that is primitive mesenchymal cells which committed early stromagenic activity.