Aim: To assess the frequency, pervasiveness, associated features, and persistence of emotional and behavioural problems in a community sample of young children with autism spectrum disorder (ASD). Method: Parents (n=277) and teachers (n=228) of 4- to 8-year-olds completed the Developmental Behaviour Checklist (DBC). Intellectual ability and autism symptomatology were also assessed. A subsample repeated the DBC. Results: Three-quarters of the cohort scored above the clinical cut-off on the Developmental Behaviour Checklist Primary Carer Version (DBC-P) questionnaire; almost two-thirds of these scored above cut-off on the Developmental Behaviour Checklist Teacher Version (DBC-T) questionnaire. In 81%, problems persisted above threshold 14 months later. Higher DBC-P scores were associated with greater autism symptomatology, higher deprivation index, parental unemployment, and more children in the home but not with parental education or ethnicity, or child's age or sex. Children with IQ>70 scored higher for disruptive behaviour, depression, and anxiety symptoms; those with IQ<70 scored higher for self-absorption and hyperactivity. Interpretation: The DBC identifies a range of additional behaviour problems that are common in ASD and which could be the focus for specific intervention. The results highlight the potential benefit of systematic screening for co-existing problems.