Familial adenomatous polyposis coli is an inherited multiple neoplasia syndrome that is associated with an increased risk for development of another primary tumor. We report a case of a 14-year-old boy who had a proctocolectomy for familial adenomatous polyposis coli. He had survived radical nephrectomy, chemotherapy, and radiotherapy for a congenital clear cell sarcoma of the right kidney. Perhaps the presence of the familial adenomatous polyposis gene induces chromosomal instability in affected persons.