There is a paucity of evidence concerning the patterns of multi-informant agreement in populations with Autism Spectrum Disorders (ASD). This study compared ratings of behaviour and emotional problems and social functioning provided by 45 adolescents aged 12-18 years, with Autistic or Asperger s Disorder with ratings by their parents and teachers. Behaviour and emotional problems were measured using the Child Behaviour Checklist and social functioning was measured with the Social Skills Rating System. Moderate agreement was found between adolescent and parent ratings of psychopathology and social functioning. In general, parent and teacher ratings and adolescent and teacher ratings differed significantly. These findings suggest that behaviour varies across environmental contexts. Patterns of agreement between multiple informants observed in the current study frequently differed from those previously found in non-ASD populations. Clinicians and researchers need to consider a multi-informant approach to obtain a detailed picture of behaviour and emotional problems in adolescents with autism and Asperger s Disorder.