Dyads of siblings in which the younger sibling had an intellectual disability (ID, n = 25) were videotaped interacting. The ID group was compared with typically developing sibling dyads matched on mental age (n = 25) and chronological age (n = 25). We observed the mediation strategies, activation, and antimediation behaviors of older siblings and younger siblings' responsiveness to mediation. Mediation strategies were analyzed by the Observation of Mediation Interaction scale. The ID group scored highest on mediation strategies and lowest on activation and antimediation behaviors. Younger siblings' responsiveness to mediation was highest among the ID group. Mediation for Intentionality and Reciprocity and Meaning were positively associated with the verbal responsiveness of the younger siblings. Activation and antimediation behaviors were negatively associated with the verbal responsiveness.