This study examined the secondary effects of Behavioral Couples Treatment (BCT) for parents with substance use disorder on youth reports of internalizing symptoms (i.e., depressive and anxiety symptoms). Participants were 59 triads (father, mothers, and youth; 32 girls, 27 boys) in which one or both parents met criteria for drug or alcohol use disorder (or both). Mothers, fathers, and youth completed pretreatment, post-intervention, and 6-month post-intervention follow-up assessments. Two piecewise latent growth models examined whether number of sessions attended was associated with parents’ relationship satisfaction or its growth over time, and in turn if parents’ relationship satisfaction was uniquely associated with youth depressive/anxiety symptoms or their growth over time. A significant indirect effect at post-intervention revealed the number of sessions attended contributed to decreases in youth depressive symptoms via increases in mothers’ and fathers’ relationship satisfaction. Mothers’ relationship satisfaction uniquely mediated the relationship between number of sessions attended and youth depressive symptoms at post-intervention. With regards to fathers, there was a non-significant trend such that increases in sessions attended was associated with decreases in youth depressive symptoms post- intervention via increasing relationship satisfaction among fathers. Findings suggest that BCT may have protective secondary effects in reducing youth reports of depressive symptoms among couples in which one or both parents have substance use disorder.