Increasing knowledge regarding the genetic basis of hereditary nephropathies has contributed much to the understanding of their pathogenesis. In addition, localization and identification of genes have offered new tools for the classification and diagnostics of hereditary nephropathies. The diagnosis at the DNA level, however, differs from classical diagnostic procedures in many respects. The current status of DNA diagnostics in hereditary nephropathies is summarized in this review, which includes a discussion of the major principles and limitations.