The current study examined relations among child temperament, peer interaction, and theory of mind (ToM) development. We hypothesized that: (1) children classified as behaviorally inhibited at 24 months would show less ToM understanding at 36 months in comparison to nonbehaviorally inhibited children; (2) children who displayed negative peer interaction behaviors in a peer dyadic interaction at 24 months would exhibit less ToM understanding at 36 months; and (3) behavioral inhibition (BI) and the degree of negative behaviors during a peer interaction would jointly influence ToM development, such that children with both heightened BI and negative peer interaction behaviors would exhibit worse ToM performance than behaviorally inhibited children who did not display negative social behaviors. Both BI and negative peer interaction behaviors were associated with passing fewer ToM tasks. The data revealed that children high in both BI and negative peer interaction behaviors passed fewer ToM tasks at 36 months of age than those high in BI and low in negative peer interactions or those low in BI.