This study examined English- and Spanish-speaking psychologists’ and psychiatrists’ opinions regarding problematic, absent and stigmatizing diagnoses in current mental disorders classifications (ICD-10 and DSM-IV), and their perceived need for a national classification of mental disorders. Answers to open-ended questions included in WHO-WPA and WHO-IUPsyS surveys were examined using an inductive content-analysis method. A total of 3,222 participants from 35 countries were included. The most problematic diagnostic group was personality disorders, especially among psychiatrists, because of poor validity and lack of specificity. Complex posttraumatic stress disorder was the most frequent diagnosis suggested for inclusion, mainly by psychologists, to better account for the distinct processes and consequences of complex trauma. Schizophrenia was the diagnosis most frequently identified as stigmatizing, particularly by psychiatrists, due to lack of public understanding or knowledge about the diagnosis. Of the 14.4% of participants who perceived a need for a national classification system, two-thirds were from Africa or Latin America. The rationales provided were that mental disorders classifications should consider cultural and socio-historical diversity in the expression of psychopathology, differences in the perception of what is and is not pathological in different nations, and the existence of culture-bound syndromes. Implications for ICD-11 development and dissemination are discussed.