This paper offers a life-course stress process perspective on maternal role strain as a ‘pain of imprisonment’ by engaging the concept of ‘family complexity’ in the context of mass incarceration I consider how the living arrangements of minor siblings (i.e., those living apart or together) during maternal incarceration functions as a form of family complexity. When minor children live apart from their siblings, they may experience more isolation which may further serve as a stressor for incarcerated mothers. A positive association between siblings living apart and maternal role strain would support a process of ‘stress proliferation’ across the prison-family interface. I investigate these connections using survey-based data on mothers with multiple minor children (n = 80) collected in 2011 from a voluntary sample of respondents housed in a federal minimum security prison in the United States. Multivariate logistic regression results indicate that minor siblings living apart during periods of maternal confinement elevates role strain among mothers (odds ratio = 3.66, p < 0.05). This connection is indicative of an ‘inter-institutional strain.’ Finally, children’s age also increases maternal role strain, but this finding is explained by sibling living arrangements during the mother’s incarceration.