Assortative mating can exert a profound influence on the phenotypic co
mposition of the population since it may result in an increase in the
frequency of the genotypes associated with extreme phenotypes. Applied
to the risk for a disorder such as substance abuse, this would mean a
possibility for an increase in the risk and severity of the disorder
in consecutive generations. This paper reviews the theoretical and emp
irical literature on mechanisms related to mate resemblance for the li
ability to substance abuse, sources and consequences of such resemblan
ce, and suggests directions for further research.