Recently, an association between cognitive disengagement syndrome (CDS), formerly sluggish cognitive tempo, and autism has been documented, but it is not known if the association is due to overlapping autism and CDS traits or if CDS is empirically distinct from autism. Mothers rated 2,209 children 4-17 years (1,177 with autism, 725 with ADHD-Combined type, and 307 with ADHD-Inattentive type) on the Pediatric Behavior Scale. Factor analysis of the Pediatric Behavior Scale items indicated that CDS and autism traits are empirically distinct from each other without cross-loading and are distinct from eight other factors (attention deficit, impulsivity, hyperactivity, oppositional behavior, irritability/anger, conduct problems, depression, and anxiety). CDS total scores were significantly higher in the autism + ADHD-Inattentive and autism + ADHD-Combined groups than in the autism, ADHD-Combined, and ADHD-Inattentive only groups with a nonsignificant difference between the latter three groups. CDS and autism are empirically distinct from each other and from other psychopathology dimensions. Overlapping traits do not explain the association between autism and CDS. Autism in combination with ADHD-Combined or ADHD-Inattentive increases the likelihood of CDS relative to youth who have autism, ADHD-Combined, or ADHD-Inattentive only. Because of the known associations between autism, CDS, and ADHD, both autism and ADHD must be assessed in CDS research and clinically to better understand and explain research findings and provide targeted clinical intervention.