INTRODUCTION: Acute postoperative cognitive dysfunction is characterized by neurocognitive dysfunction and confusion. In this study, we compared the cognitive status of a geriatric population undergoing cognitive dysfunction, as assessed by the Short Portable Mental Status Questionnaire (SPMSQ) before and after ketamine administration. METHODS: Sixty patients were enrolled for the study  and they were randomly selected for double–blind study to receive either ketamine (0.3 mg/kg dose) or physiologic solution (control group). Fifty seven(control, n = 29; ketamine, n = 28) patients completed the trial. Cognitive performance was assessed with an abbreviated version of the SPMSQ. Measurements of analgesia, sedation, and hemodynamic variables were recorded. RESULTS: With respect to cognitive performance, the baseline evaluation was similar for the control and ketamine groups. Postoperative evaluation showed an improvement only in the ketamine group. The average dose of midazolam was higher in the control group, but the difference was not clinically significant. After surgery, analgesic behavior was better in the ketamine group than in the control group. There were no differences between groups in the sedation scale or in hemodynamic variables. CONCLUSIONS: The administration of 0.3 mg/kg ketamine during day care surgery in geriatric patients changed their cognitive status as assessed by the SPMSQ, decreased the required dose of anesthetics, and in hemodynamic variables.