Objective: This study examines relations between the severity of specific symptoms of schizophrenia spectrum disorder (SSD) and severity of the three defining symptom domains of autism spectrum disorder (ASD) in children with ASD (N = 147) and child psychiatry outpatient referrals (Controls; N = 339). Method: Participants were subdivided into four groups depending on ASD status (plus or minus) and whether they met symptom criteria for attention-deficit/hyperactivity disorder (plus or minus ADHD). Their mothers and teachers evaluated them with a "DSM-IV"-referenced rating scale. Results: Correlations between schizoid personality symptoms and ASD social skills deficits were moderate to large, and this was true for children with ASD and Controls, regardless of ADHD status, and for mother's and teachers' ratings. Conversely, severity of hallucinations, delusions, and disorganized thinking were minimally correlated with ASD severity with the exception of Controls with ADHD. The disorganized behavior and negative symptoms of schizophrenia evidenced the strongest pattern of associations with ASD symptoms, and this was particularly true for children with co-morbid ADHD (plus or minus ASD, all three ASD symptom dimensions), and for teachers' ratings of all four groups. Nevertheless, there was considerable variability in relations for specific symptoms across informants and groups. Correlations between SSD symptom severity and IQ were generally low, particularly among the ASD Only group and for all teacher-rated symptoms. Conclusion: Associations between ASD and SSD symptoms were often dimension-specific, and this was particularly evident in children without ADHD (plus or minus ASD; mothers' ratings). Findings were interpreted as supporting the deconstruction of complex clinical phenotypes as a means of better understanding interrelations among psychiatric syndromes. (Contains 4 tables.)