Background: Differences in the ICD-10 and DSM-IV definitions for the same disorder impede international communication and research efforts. The forthcoming parallel development of DSM-V and ICD-11 offers an opportunity to harmonise the two classifications.
Aims: This paper aims to facilitate the harmonisation process by identifying diagnostic differences between the two systems.
Method: DSM-IV-TR criteria sets and the ICD-10 Diagnostic Criteria for Research were compared and categorised into those with identical definitions, those with conceptually based differences and those in which differences are not conceptually based and appear to be unintentional.
Results: Of the 176 criteria sets in both systems, only one, transient tic disorder, is identical. Twenty-one per cent had conceptually based differences and 78% had non-conceptually based differences.
Conclusions: Harmonisation of criteria sets, especially those with non-conceptually based differences, should be prioritised in the DSM-V and ICD-11 development process. Prior experience with the DSM-IV and ICD-10 harmonisation effort suggests that for the process to be successful steps should be taken as early as possible.