We analyze how siblings interact when deciding informal care provision to their elderly parent. We consider a non-cooperative model of the children’s care decisions, allowing productivity of care provision to vary with the child’s gender. We show that this implies that the strategic interaction effects depend on the siblings’ gender composition. The theory leads to a simultaneous bivariate tobit model. Estimation results suggest that sons’ and daughters’ free-riding behavior is significantly larger when the sibling is a sister. This is in line with a higher care provision productivity for women and can explain why women more often provide informal care than men do.