We report the results of carrier and prenatal diagnosis for hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency, Lesch-Nyhan syndrome, by carrier testing of 83 women and prenatal analysis of 26 pregnancies. Our diagnostic methodologies include mutation detection and linkage analysis for probands and their families and biochemical measurement of HPRT enzyme activity for at-risk pregnancies. Identification of the mutation in the index case of each family permits precise carrier diagnosis using polymerase chain reaction (PCR) amplification of HPRT gene sequences and automated DNA sequencing. We demonstrate 100 per cent sensitivity for the detection of mutations in the HPRT gene of affected males and highly efficient carrier testing of at-risk females. Two other molecular methods proven to have high utility include PCR-based dosage analysis and linkage analysis by PCR amplification of a short tandem repeat (STR) in intron 3 of the HPRT gene. As a result, 45 at-risk women, 56 per cent of those tested, were identified not to be carriers of their family's HPRT gene mutation. Seven of these women were the mothers of affected males and prenatal testing for future pregnancies was recommended because of the possibility of gonadal mosaicism. Thirty-eight of these women were more distant relatives of affected males, thereby eliminating the need for future prenatal procedures. These studies illustrate the utility and precision of molecular methodologies for carrier and prenatal diagnosis of Lesch-Nyhan syndrome. These studies also illustrate that molecular diagnostic studies of affected males and carrier testing prior to pregnancy can clarify genetic risk predictions and eliminate unnecessary prenatal procedures.