Enhancing clinical utility is an emphasis of the World Health Organization's development of the mental and behavioural disorders chapter of the next International Classification of Diseases (ICD-11). Understanding how clinicians conceptualize the structure of mental disorders can enable a more clinically intuitive classification architecture that will help professionals find the categories they need more efficiently. This study examined clinicians' conceptualizations of the relationships among mental disorders and the dimensions they use in making these judgements. Psychiatrists and psychologists from 64 countries (n = 1,371), participating in English or Spanish, rated the similarity of mental and behavioural disorders presented as paired comparisons. Data were analysed by multidimensional scaling procedures (INDSCAL) and by analyses of consistency. Participants used three distinctive dimensions to evaluate the similarity among disorders: internalizing versus externalizing, developmental versus adult onset, and functional versus organic. Clinicians' conceptual map of mental disorders was rational and highly stable across profession, language, and country income level. The proposed ICD-11 structure is a moderately better fit with clinicians' conceptual model than either ICD-10 or DSM-IV. Clinician judgements can be used to improve clinical utility of the ICD-11 without sacrificing validity based on a scientific approach to enhancing a logically organized classification meta-structure.