The validity of the Parental Concerns Questionnaire, a brief screening checklist assessing the presence and severity of 13 developmental and behavioral concerns expressed by parents of children with autism spectrum disorders, was determined in 53 children ages 4 to 10 years with a clinical diagnosis of autism spectrum disorder and 48 age-matched typically developing controls. Parents completed the Parental Concerns Questionnaire, the Child Behavior Checklist, the Child Sleep Habits Questionnaire, and either the Repetitive Behavior Scale or the Compulsive Behavior Checklist. A clinical examiner administered the Peabody Picture Vocabulary Test and the Autism Diagnostic Observation Scale. The Parental Concerns Questionnaire demonstrated high internal consistency in the autism spectrum disorder subgroup. Reliability and stability over time were demonstrated. Analyses showed variability in item responses for each child indicating that parents were not globally answering all items as concerns. Comparison of Parental Concerns Questionnaire item scores to scores for similar multiquestion domains on standardized parent-rated and clinician-administered assessment tools demonstrated external validity with other parent-rated and clinician-rated instruments. The Parental Concerns Questionnaire is a reliable screening instrument to assess parentally reported developmental and behavioral symptoms in children with autism spectrum disorders.