The authors of the Childhood Autism Rating Scale (CARS) state in the manual that the best cutoff score for distinguishing low functioning autism (LFA) from intellectual disability is 30 for children and 28 for adolescents and adults. This study determined that a cutoff score of 25.5 was most accurate in differentiating between high functioning autism or Asperger syndrome (HFA; n = 197) and ADHD (n = 74) in a sample of 1- to 16-year-olds with IQs of 80 or higher. Classification accuracy was 96% using clinician scores and 72% using parent scores. Children with LFA (n = 193) had significantly higher clinician and parent scores than children with HFA, and scores were negatively correlated with IQ. None of the typical children (n = 64) earned parent scores greater than 21.