We investigated the congruent and criterion validity of the Aberrant Behavior Checklist (ABC) in a clinical sample of toddlers seen over 1 year in Turkey. All consecutive patients (N = 93), 14-43 months old (mean, 30.6 mos.), in a child psychiatry outpatient clinic were included. The ABC, Autism Behavior Checklist (AuBC), and Child Behavior Checklist 2/3 (CBCL) were completed by the children's parents. Internal consistency for ABC subscales was moderate to high. The total ABC score, which is interdependent with subscales (e.g., Irritability, Social Withdrawal) of the ABC, was significantly correlated with the CBCL-total (r = 0.73) and AuBC-total (r = 0.71) scores. Subscales of the ABC revealed significant differences between diagnostic groups. ABC Total, and the Irritability and Hyperactivity subscale scores, were significantly higher in children with externalizing disorders; the Lethargy/Social Withdrawal and Stereotypic Behavior subscale scores were significantly higher in toddlers with autism. The ABC appears to be capable of discriminating several syndromes, such as disruptive behavior disorders and autism in early childhood.