Background: ICD-10 and DSM-IV include similar criterial symptom lists for conduct disorder (CD) and oppositional defiant disorder (ODD), but while DSM-IV treats each list separately, ICD-10 considers them jointly. One consequence is that ICD-10 identifies a group of children with ODD subtype who do not receive a diagnosis under DSM-IV. Methods: We examined the characteristics of this group of children using the Great Smoky Mountains Study of children in the community aged 9-16. This study provided child and parent reports of symptoms and psychosocial impairment assessed with standardised diagnostic interviews. Results: Children who received an ICD-10 diagnosis but not a DSM-IV diagnosis showed broadly similar levels of psychiatric comorbidity, delinquent activity and psychosocial impairment to those who met DSM-IV criteria in both cross-sectional and longitudinal analyses. Conclusions: These results indicate that DSM-IV excludes from diagnosis children who receive an ICD-10 diagnosis of CD (ODD sub-type), and who are substantially disturbed. Methods of redressing this situation are considered.