Methods for isolating patched genes, particularly mammalian patched genes, including mouse and human patched genes, as well as invertebrate patched genes and sequences, are provided. Loss-of function of the patched is associated with the occurrence of human cancers, particularly basal cell carcinomas of the skin. The cancers may be familial, having as a component of risk an inherited genetic predisposition, or may be sporadic. Therefore, methods for using the patched gene as a diagnostic for assessing a genetic predisposition to cancer, and to identify specific cancers having mutations in this gene, are disclosed.