Introduction: The study aim was to describe behaviours associated with autistic traits. Methods: The Childhood Behaviour Checklist (CBCL) and Social Communication Questionnaire (SCQ) were used as measures of behaviour and autistic traits respectively in 331 adolescents receiving educational support. CBCL scores were compared between three groups defined by SCQ score: autism, pervasive developmental disorder (PDD) and non-PDD. Results: The PDD and autism groups had significantly higher scores on the CBCL than the non-PDD group across all CBCL scales except Delinquent Behaviour. On seven of the eight scales, there was no difference between the autism and PDD groups. Conclusion: Those with PDD or autism display significantly higher levels of withdrawal, somatic complaints, anxiety/depression, social, thought and attention problems, and aggressive behaviour.