The developmental significance of preschool children's imaginary companions was examined. Mothers of 78 children were interviewed about their children's social environments and imaginary companions (if their children had them). Results revealed differences between invisible companions and personified objects (e.g., stuffed animals or dolls) in terms of the pretend friends' stability and ubiquity, identity, and relationship with the child. Relationships with invisible companions were mostly described as sociable and friendly, whereas personified objects were usually nurtured. Mothers reported that personification of objects frequently occurred as a result of acquiring a toy, whereas invisible friends were often viewed as fulfilling a need for a relationship. Compared to children without imaginary companions, children with imaginary companions were more likely to be firstborn and only children.