Sensitivity to alcohol may influence the severity of ethanol teratogenesis. To examine this hypothesis, the teratogenic effects of ethanol were compared in Long-Sleep (LS) and Short-Sleep (SS) mice, selectively bred for differences in ethanol-induced narcosis. Inbred C57BL/6J (B6) mice were included to confirm previously reported teratogenic effects using our own treatment regimen and standard assessment technique. Intragastric administration of ethanol (5.8 g/kg) on Days 9 and 10 of pregnancy resulted in growth retardation and an increase in prenatal mortality in LS litters but not in SS litters. Therefore, alcohol sensitivity plays a role in the severity of prenatal alcohol effects. B6 mice showed more ethanol teratogenicity than either LS or SS mice, even though maternal blood ethanol levels were similar across genotypes. This result suggests genetic variations other than alcohol sensitivity also influence ethanol teratogenesis.