Relations between interior self-knowledge and (a) imaginary companion (IC) status and (b) theory of mind (ToM) abilities were investigated in a sample (N= 80) of 4- to 7-year-olds. Interior self-knowledge was assessed in terms of the extent to which children acknowledged that they (rather than an adult) were the authority on unobservable aspects of themselves (e.g., dreaming, thinking, hunger). Compared with children without an IC, those who possessed a parentally corroborated IC ascribed less interior self-knowledge to an adult, with a trend for them to assign more interior self-knowledge to themselves. Children's interior self-knowledge judgments were not associated with their ToM performance. IC status was also unrelated to ToM performance. We consider how having an IC may provide children with opportunities to distinguish between knowledge that is inaccessible to an external observer and that which an external observer may glean without being told.