Poor marital quality is a reliable correlate of internalizing problems, but the etiology of this association has yet to be examined. Marital distress may exert its influence by acting as a stressor that enables the expression of latent genetic risk for internalizing psychopathology. The authors examined this question using 379 twin pairs, assessed for marital quality, symptoms of major depression (MD), generalized anxiety disorder (GAD), panic attacks (PA), and neuroticism (N). A phenotypic factor analysis confirmed that one factor best accounted for the variance shared between MD, GAD, PA, and N. After accounting for genetic influences on the general Internalizing factor, there were residual genetic influences on N but no specific genetic influences on any other individual internalizing syndrome. The authors found overlap between the genetic influences on marital quality and the internalizing spectrum. Finally, biometrical moderation models revealed that genetic effects on the Internalizing factor increased as the marital quality deteriorated (marital quality high: h2 = 0.05; marital quality low: h2 = 0.29), suggesting that those with a genetic predisposition to internalizing syndromes may be more likely to express this predisposition in the context of a dissatisfying marriage.