OBJECTIVES: Previous studies have shown that the endogenous opioid system, which plays an important role in drinking behavior, might be related to the genetic etiology of alcohol dependence. And a recent study reported that the affinity of micro opioid receptor, which is closely related to the endogenous opioid system activity, is affected by the genotype of micro opioid receptor gene (OPRM1) A118G. To investigate the gender difference in genetic etiology of alcohol dependence, this study examined the association of the genotype of OPRM1 A118G with female alcohol dependence in Koreans. METHODS: The author studied the genotype of OPRM1 A118G in 106 male and 35 female Korean with alcohol dependence and 80 male and 60 female healthy Koreans as control. RESULTS: 1) A statistically significant increase in A/G or G/G (G+) genotype of OPRM1 A118G was observed in women with alcohol dependence compared to the controls. 2) Among men with alcohol dependence, no significant difference in OPRM1 A118G polymorphism was observed relative to the age at which drinking started, age of onset of alcohol-related problems, age of first admission to psychiatric hospital for alcohol-related problems, drinking days per month, drinks per drinking day, family history of alcohol dependence in the first-degree relatives or history of severe alcohol withdrawal symptoms. But the drinking days per month is significantly less in those who have A/G or G/G genotypes of OPRM1 A118G. CONCLUSION: These results suggest that G+ genotypes of micro opioid receptor gene A118G are important genetic factors in the etiology of female alcohol dependence.