ABSTRACT: BACKGROUND: The 17-item Hamilton Depression Rating Scale (HAM-D17) remains the 'gold standard' for measuring treatment outcomes in clinical trials of depressed patients. The Montgomery Asberg Depression Rating Scale (MADRS), Clinical Global Impressions-Severity (CGI-S) and -Improvement (CGI-I) scales are also widely used. OBJECTIVE: This analysis of data from 22 double-blind, placebo-controlled clinical studies of venlafaxine in adult patients with major depressive disorder was aimed at assessing correlations among these 4 scales. METHODS: Changes from baseline for MADRS, HAM-D17 and CGI-S, and end point CGI-I scores and response (>/=50% decrease from baseline HAM-D17 or MADRS, or CGI-S or CGI-I score </=2) were analysed. Pearson correlation coefficients were calculated for all pairs of the four scales (HAM-D17/MADRS, HAM-D17/CGI-S, HAM-D17/CGI-I, MADRS/CGI-S, MADRS/CGI-I, CGI-S/CGI-I) at different time points. Effect sizes were calculated using the Cohen d. RESULTS: Correlations were significant at all time points (p < 0.0001), increased over the course of treatment, and were similar across treatment groups. Effect sizes ranged from 0.31 to 0.42; MADRS and CGI-I effect sizes were slightly greater compared with HAM-D17 or CGI-S for continuous measures and response. CONCLUSION: Although MADRS and CGI-I were more sensitive to treatment effects, HAM-D17, MADRS, CGI-S and CGI-I scores present a consistent picture of response to venlafaxine treatment.