The current study examines whether the dopamine transporter (DAT1) VNTR polymorphism and paternal alcoholism are related to serious alcohol problems. Using data from the National Longitudinal Study of Adolescent Health (Add Health), we found that the DAT1 polymorphism interacted with paternal alcoholism to predict serious alcohol problems among males. Specifically, the 10-repeat allele conferred an increase of alcohol problems only among males who also had an alcoholic father; the 10-repeat allele was unrelated to alcohol problems for males without an alcoholic father. Coefficient tests revealed that this interaction effect was stronger among African-American males. Females who possessed the 9-repeat allele were more likely to report serious alcohol problems, but this effect was not moderated by paternal alcoholism. These analyses suggest that additive and interactive effects of DAT1 and paternal alcoholism may operate differently across genders and races.