Childhood Autism Rating Scale (CARS) and Autism Behavior Checklist (ABC) are tests widely used for screening and diagnosis of autism. This study verified their correspondence and conflict with a diagnosis made with DSM-IV criteria. The sample consisted of 65 children, aged 18 months to 11 years. We found complete agreement between DSM-IV and CARS. We show that ABC does not distinguish individuals with autistic disorders from other cases of developmental disorders as well as CARS: the number of false negatives is high (46%) with ABC as opposed to 0% with CARS.