Objective: This study compared the differential severity of specific symptoms of schizophrenia spectrum disorder (SSD) in children with autism spectrum disorder (ASD) and child psychiatry outpatient referrals (controls). Each group was further subdivided into subgroups with and without co-occurring attention-deficit/hyperactivity disorder (ADHD). Method: Children with ASD (n = 147) and controls (n = 335) were evaluated with parent and teacher versions of a psychometrically established DSM-IV-referenced rating scale. Results: The two ASD groups (with and without ADHD) had a larger number of more severe SSD symptoms than their respective control groups (with and without ADHD), extending the observation of an association between ASD and SSD to subgroups with and without co-occurring ADHD. The ASD groups exhibited more severe schizoid personality symptoms than controls, but findings for schizophrenia symptoms were mixed. The ASD + ADHD group generally had more severe disorganized thought, disorganized behavior, and negative schizophrenia symptoms than controls (with and without ADHD); nevertheless, findings varied according to ADHD status (present versus absent), individual symptom (symptom specificity), and informant (informant specificity). Ratings of hallucinations and delusions indicated mild severity and few group differences. Negative symptoms such as inappropriate emotional reactions evidenced considerable group divergence. Conclusion: Findings provide additional support for an interrelation between ASD and SSD symptoms and the differential influence of neurobehavioral syndromes on co-occurring symptom severity, underscore the multidimensionality of SSD in children with ASD, and suggest how symptom phenotypes may contribute to a better understanding of the etiology, nosology, and possibly clinical management. (Contains 3 tables.)