Autistic youth often experience challenges in interactions with neurotypical peers. One factor that may influence successful interactions with peers is interpersonal synchrony, or the degree to which interacting individuals align their behaviors (e.g. facial expressions) over time. Autistic and neurotypical youth were paired together into three dyad types: autistic participants paired with autistic participants (AUT-AUT), autistic participants paired with neurotypical participants (AUT-NT), and neurotypical participants with neurotypical participants (NT-NT). Dyads participated in a free conversation task and a video-watching task. We tested whether smiling synchronization differed between AUT-AUT, AUT-NT, and NT-NT dyads. We further tested if smiling synchronization predicted youth-reported interaction enjoyment. AUT-NT dyads had significantly reduced smiling synchronization compared with NT-NT dyads. Smiling synchronization also predicted multiple aspects of participant-rated interaction enjoyment, such as the desire to interact with the peer partner again, above and beyond the overall amount of smiling in the interaction. These findings indicate links between smiling synchronization and interaction enjoyment for autistic and neurotypical youth. Identifying opportunities to synchronize or share positive affect in interactions may promote more enjoyable interactions for both autistic and neurotypical youth.