Este artigo está licenciado sob forma de uma licença Creative Commons Atribuição 4.0 Internacional, que permite uso irrestrito, distribuição e reprodução em qualquer meio, desde que a publicação original seja corretamente citada. ABSTRACT AIMS: To verify if there are changes in the decision-making capacity of elderly patients with major depression. METHODS: This is a prospective cohort study with an initial cross-sectional analysis conducted between January 2014 and September 2015. Treatment-naïve elderly patients from the Cerebral Aging Outpatient Clinic at PUCRS São Lucas Hospital, in Porto Alegre, Brazil, all diagnosed with major depressive disorder, were selected. The control group was composed of elderly individuals from the same community who had neither depression nor cognitive problems. For evaluation of the decision-making capacity, the Assessment Scale for Decision-Making Capacity was designed and validated in a previous stage of the research. This instrument is divided into four domains: daily activity, financial management, self-management, and well-being. The Geriatric Depression Scale (short version) and the Mini-International Neuropsychiatric Interview (detailed version) were used to evaluate the presence of depression. The Vellore Screening Instrument for Dementia and the Addenbrooke's Cognitive Examination (revised version) were applied to evaluate cognitive decline. Decision-making capacity was compared between the two groups of elderly individuals. The same evaluation was conducted with elderly patients with depression after six months of psychiatric treatment. The statistical analysis included Student's t, Pearson's chi-square, Mann-Whitney, and Wilcoxon tests. Statistical significance was set at p≤0.05. RESULTS: Forty-eight elderly patients with major depression and 144 elderly individuals from the control group participated in the study. The Assessment Scale for Decision-Making Capacity average score in depression patients was 70.5±17.9, compared to 94.6±9.6 (p<0.001) in the control group, which indicates poorer decision-making capacity among patients with major depression. The domains with the most striking differences in the average scores were self-management (depression patients 65.0±23.3 and control group 97.8±6.2) and well-being (depression patients 52.2±27.1 and control group 91.8±16.7). When comparing patients with depression before and after treatment, regarding both the general score and the four domains of the Assessment Scale for Decision-Making Capacity, the decision-making capacity was higher after the treatment. CONCLUSIONS: The group of elderly patients with current major depression had a lower decision-making capacity compared to the control group. Their decision-making capacity improved after six months of psychiatric treatment.