Objectives. To characterize the clinical, pathologic, and genetic aspects of patients with a previously undescribed phenotype of testicular germ cell tumors associated with renal hypoplasia or agenesis and urethral hypospadias. Methods. Review of clinical and pathologic findings and genetic analysis of constitutional and tumor DNA for mutations of the Wilms' tumor suppressor gene (WT1). Results. Clinical findings suggest that this phenotype is distinct from other syndromes associated with renal anomalies and that the associated testicular tumors are histologically and clinically similar to those that occur sporadically. No karyotypic abnormalities, loss of heterozygosity, or mutations in the zinc finger domains (exons 7-10) of WT1 were observed in 5 patients with this phenotype. Conclusions. The phenotype of testicular germ cell tumor, developmental renal anomalies, and urethral hypospadias constitutes a discrete syndrome caused by a gene distinct from WT1.