OBJECTIVES: The Clinical Global Impression-Schizophrenia Scale was designed to assess severity and treatment response in subjects with schizophrenia involved in naturalistic studies and daily clinical practice. The objective of this study is to validate the Portuguese version of the Clinical Global Impression-Schizophrenia Scale in Brazil by assessing its psychometric properties. METHOD: Cross-sectional validation study of the Portuguese version of the Clinical Global Impression-Schizophrenia Scale, tested in outpatients and inpatients with schizophrenia (DSM-IV, ICD-10) from 6 centers in Brazil. Concurrent validity and sensitivity to change were assessed by comparison with the Positive and Negative Syndrome Scale, which is considered the gold standard tool to evaluate patients with schizophrenia. Interrater reliability was evaluated by intraclass correlation coefficients (ICC) calculated based on the scoring of two concomitant raters. RESULTS: 70 inpatients and 70 outpatients were evaluated. Total Clinical Global Impression-Schizophrenia Scale and Positive and Negative Syndrome Scale scores were highly correlated (r=0.79; p<0.01). Positive (r=0.86), negative (r=0.79), depressive (r=0.66) and cognitive (r=0.75) symptoms subscale scores were also correlated between both scales (p<0.01). Sensitivity to change was significantly correlated between the Clinical Global Impression-Schizophrenia Scale and Positive and Negative Syndrome Scale (r=0.73; p<0.01). Interrater reliability was substantial for positive symptoms and total scores of the Clinical Global Impression-Schizophrenia Scale (ICC=0.81 and 0.73), and moderate for negative, depressive, and cognitive symptoms score (0.64, 0.67 and 0.63, respectively). CONCLUSIONS: The Brazilian version of the Clinical Global Impression-Schizophrenia Scale is a valid and reliable instrument for the assessment of severity and treatment response in schizophrenic inpatient and outpatients.