The editorial by Andrews et al (1999) usefully calls attention to issues of compatibility between diagnostic classification systems but we believe that the editorial greatly overstates the compatibility problem as well as its implications. The article begins with the suggestion that the DSM–IV authors' position is to downplay the differences between DSM–IV and ICD–10. After stating that the American Psychiatric Association “felt sufficiently confident to publish a DSM–IV International Version in which the DSM–IV criteria are listed against the ICD–10 codes”, the authors go on to report concordances between the classifications for the main mental disorders as ranging from a low of 33% (for substance harmful use or abuse) to 87% (for dysthymia), with an overall concordance of only 68%. The authors conclude that if this “unnecessary dissonance between the classification systems continues, patients, researchers and clinicians will be all the poorer”. Although we acknowledge that there are a number of differences between the two systems, the authors fail to assess fully the sources, significance and solutions for this compatibility problem.