Children with autism spectrum disorders (ASD) are at high risk for co-occurring psychiatric disorders. Previous research has suggested that restricted and repetitive behaviors (RRB) are associated with symptoms of co-occurring psychiatric disorders in individuals with ASD, but this relationship is not well understood. The current study investigated the relationship between RRB and co-occurring psychiatric symptoms, including depressive, anxiety, attention-deficit hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) symptoms, while considering the role of level of functioning. Participants were 72 parents of youth diagnosed with an ASD (ages 5-17). They completed the Social Communication Questionnaire (SCQ), the Repetitive Behavior Scale-Revised (RBS-R), an abridged version of the Child Symptom Inventory-4 (CSI-4) and the Conceptual domain of the Adaptive Behavior Assessment System, 2nd Edition (ABAS-II). Results indicated that RRB do predict psychopathology. Ritualistic and sameness behavior is predictive of anxiety, depression and ODD while stereotypy is predictive of ADHD. Restricted interests were a negative predictor of depression. Level of functioning moderated the relationship between self-injurious behavior (SIB) and both anxiety and depressive symptoms as well as the relationship between ritualistic and sameness behavior and depressive symptoms. Understanding the relationship between RRB and psychiatric symptoms could help clarify the presentation of ASD phenotypes as well as etiological variables. (Contains 3 tables and 3 figures.)