The drinking behavior, alcohol-induced facial flushing and ALDH2 genotypes were determined in 283 Thai men comprising 85 who were alcohol-dependent, 62 hazardous/harmful drinkers and 136 non-drinkers or infrequent drinkers. A structured interview questionnaire, containing the 'tri-level' method and the Alcohol-Use Disorders and Associated Disabilities Schedule, was used to determine the quantity of drinking and the number of alcohol-related adverse experiences. The study revealed the mutant ALDH2*2 allele in 44 (15.5%) subjects. The risks of being alcohol-dependent and of having hazardous/harmful drinking were lower in individuals with heterozygous ALDH2*1/*2, compared with homozygous ALDH2*1/*1 [relative probability ratios (95% CI) 0.14 (0.05-0.41) and 0.23 (0.08-0.61), respectively]. Eighty percent of those who were heterozygous and 28% of those who were homozygous ALDH2*1 reported flush symptoms after drinking alcohol. Twenty-nine percent of homozygous ALDH2*1 individuals, but only 9% of heterozygous subjects, drank almost everyday (24-30 days/month). Similarly, higher percentages of people drinking beyond the safety limit (>60 g/day) and having alcohol-related problems were observed in homozygous ALDH2*1 compared with heterozygous individuals: 32% vs. 5% and 27% vs. 12%, respectively. Overall, the study supports the role of the mutant ALDH2*2 allele in preventing high alcohol consumption and the development of alcohol dependence in a Thai population.