Formal thought disorder (FTD) is a disruption in the flow of thought and a common feature in psychotic disorders and autism spectrum disorder (ASD). Executive dysfunction has often been associated with FTD, yet for ASD convincing evidence is lacking. This study investigated FTD and three core executive functions in 50 young children and adolescents with high-functioning ASD and 56 matched controls. Higher overall levels of FTD marked ASD compared to controls. Furthermore, in ASD decreased performance on verbal working memory was correlated with increased FTD ratings and explained a significant amount of variance of objective and subjective FTD. Verbal working memory is currently the most promising target executive function for understanding the development of idiosyncratic thought disorders in ASD.