Testicular germ-cell tumours (TGCT) are the most common neoplasm in young men. Various studies have suggested the existence of an inherited predisposition to development of these tumours. Genome-wide screens subsequently provided evidence of a TGCT susceptibility gene on chromosome Xq27 (TGCT1) that might also predispose to cryptorchism. However, this putative gene has yet to be identified, and other TGCT susceptibility genes probably exist. Completion of the human gene map and advances in genetic research will facilitate further investigation of genetic predisposition to TGCT. Insight into inheritance of TGCT might lead to the identification of individuals at increased risk of developing the disorder, increase our understanding of the mutation pathways that lead to sporadic cases, and contribute to improvement in diagnosis and treatment. Clinicians should record the family history of cancer and urogenital differentiation defects in patients with TGCT.