The present paper critiques the current diagnostic criteria from the DSM-III-R and the draft criteria proposed for the ICD-10 for attention deficit hyperactivity disorder (ADHD). Improvements made in the criteria over earlier editions are discussed along with continuing limitations in these approaches to clinical diagnosis. The issue of whether ADHD constitutes an actual syndrome is also reviewed. It is concluded that despite contradictory evidence for covariation of the symptoms, the disorder meets other important conditions for syndrome definition and should continue to be viewed as such. The variability of symptoms across settings and parameters which may affect this variability are briefly noted as is the impact of this symptom instability on establishing diagnostic criteria. A number of suggestions for revision of these criteria are provided that can be incorporated into current clinical and research practices to improve the rigor and discriminative validity of the criteria for ADHD. The implications of these revisions for clinical diagnosis are also discussed.