Disentangling shared genetics and environments from family members influence is difficult. This paper estimates sibling spillovers by exploiting a double random assignment in a decision that has life-long implications: military service. Our results provide new and rare evidence on the importance of family networks. We find that having an elder brother inducted into the military increases the younger brother’s service probability by 8 percent. This substantial spillover effect runs only from the elder to the younger brother. The most likely mechanism is the information channel, in which interpersonal dominance plays a role.