Hallucination and dissociation have been found to be associated with imaginary friend play in childhood (CIC). Past studies have not investigated how this play relates to adult prodromal symptoms or how childhood adversity mediates the relationship. CIC play was examined in 278 participants, 18–24 years. CIC status predicted prodromal symptoms of hallucination only, whereas childhood adversity predicted all other symptoms. Mediation analysis found CIC’s relation to hallucination symptoms was partially mediated by childhood adversity. Findings fit with views that CIC are a positive childhood experience which may convert to a negative developmental trajectory through the impact of childhood adversity.