A common inherited RFLP of the L-myc proto-oncogene has been reported to correlate with cancer susceptibility or prognosis for some tumors. Using a PCR-based RFLP assay on DNA extracted from peripheral blood samples, we determined the L-myc EcoRI genotype of patients with HCC, patients with other liver tumors, and healthy controls. In this polymorphism there are 2 alleles, L and S, which define 3 possible genotypes: LL, LS, and SS. While the genotype distribution of patients with other liver tumors and healthy controls do not differ from one another, both differ significantly from the genotype distribution of patients with HCC. This difference is primarily the result of a low frequency of the SS genotype among HCC patients compared to controls or other liver tumor patients. Persons with the SS genotype appear to be protected against HCC and have roughly one-ninth the risk of persons who carry one or more copies of the L allele. Within HCC cases, patients with different L-myc genotypes show slight, but not statistically significant, differences in tumor characteristics and survival.