Using data from 4,744 full, twin, half-, adopted, and stepsiblings in the Wisconsin Longitudinal Study, I examine psychological consequences of motherhood and fatherhood in midlife. My analysis includes between-family models that compare individuals across families and within-family models comparing siblings from the same family to account for unobserved genetic and environmental endowments that may confound the relationship between parenthood and mental health. Further, I examine whether the psychological effect of parenthood varies among different types of sibling dyads. The findings reveal that parenthood has similar psychological implications for middle-aged mothers and fathers. Main differences arise from specific configurations of the parental role. The association between parenthood and mental health partly reflects genetic influences but not shared early-life environment.