Previously, we described a family with renal cell carcinoma (RCC) and a constitutional balanced t(2;3) (q35;q21). Based on loss of heterozygosity and von Hippel-Lindau (VHL) gene mutation analyses in five tumor biopsies from three patients in this family, we proposed a multistep model for RCC development in which the familial translocation may act as a primary oncogenic event leading to (nondisjunctional) loss of the translocation-derived chromosome 3, and somatic mutation of the VHL gene as a secondary event related to tumor progression. Here, we describe the cytogenetic and molecular analysis of three novel tumors at early stages of development in two members of this family. Again, loss of derivative chromosome 3 was found in two of these tumors and a VHL mutation in one of them. In the third tumor, however, none of these abnormalities could be detected. These results underline our previous notion that loss of derivative chromosome 3 and VHL gene mutation play critical roles in familial RCC. In addition, they show that both anomalies may occur at relatively early stages of tumor development.