The World Health Organization Disability Assessment Schedule (WHODAS) 2.0 Brazilian version was self-applied in 500 psychiatric and 50 non-psychiatric patients in an outpatient medical centre. The instrument was reapplied in 50 psychiatric patients whose treatment with psychotropics was not altered, and in 100 whose it was altered. Confirmatory factor analysis confirmed the theoretical dimensional model proposed by the WHO for the WHODAS 2.0 36-item scale, and a simpler alternative model for the WHODAS 2.0 12-item scale. All the items of the WHODAS 2.0 was proven to be valid and reproducible for use in people with mental disorders from Brazil. The WHODAS 2.0 scores differentiate psychiatric from non-psychiatric patients and exhibited a significant correlation with the Global Assessment of Functioning scale. However, the 12-item scale was more responsive to changes in the patients' treatment than the 36-item scale, and this should be considered for Diagnostic and Statistical Manual of Mental Disorders.