BackgroundA prominent diagnostic criterion of autism spectrum disorder (ASD) relates to the abnormal or diminished use of facial expressions. Yet little is known about the mechanisms that contribute to this feature of ASD.MethodsWe showed children with and without ASD emotionally charged video clips in order to parse out individual differences in spontaneous production of facial expressions using automated facial expression analysis software.ResultsUsing hierarchical multiple regression, we sought to determine whether alexithymia (characterized by difficulties interpreting one’s own feeling states) contributes to diminished facial expression production. Across groups, alexithymic traits—but not ASD traits, IQ, or sex—were associated with quantity of facial expression production.ConclusionsThese results accord with a growing body of research suggesting that many emotion processing abnormalities observed in ASD may be explained by co-occurring alexithymia. Developmental and clinical considerations are discussed, and it is argued that alexithymia is an important but too often ignored trait associated with ASD that may have implications for subtyping individuals on the autism spectrum.