This study examined relations among preschoolers' sibling-directed internal state language, perspective-taking abilities, and sibling-directed affective behaviors in 32 sibling dyads (aged 14 months and 3-4 years) during naturalistic home observations. Preschooler references about internal states (emotions, wants, abilities) were significantly more likely to be (a) about the toddler than the self, and (b) made in the mother's absence and during sibling conflict and play. Relative to poor perspective takers, skillful perspective takers (a) engaged in more instances of internal state discourse and (b) talked more frequently about both the toddler and themselves. Preschoolers engaging in high levels of positive affective behavior also spoke more frequently about internal states than children engaging in low levels of positive affective behavior. Discussion of results highlights the notion that internal state language may be one way of regulating sibling interaction and also a potential means for siblings to construct shared meanings about their world.