To compare the impact of a pharmacist's presence for the detection of drug-related problems (DRP) in an interdisciplinary geriatric-ambulatory clinic with a control group without a pharmacist.<br/> DESIGN: Retrospective quasi-experimental study.<br/> SETTING: A geriatric ambulatory-care clinic of a 772-bed tertiary-care teaching hospital in Montreal, Canada.<br/> PARTICIPANTS: A total of 227 ambulatory patients 65 years of age and older presenting to their appointment at the geriatric ambulatory clinic between May 1, 2018, and April 30, 2019.<br/> MAIN OUTCOME MEASURE(S): DRP detected by the interdisciplinary team during the patient evaluation process. Data were collected from clinical notes written by the health care professionals in the electronic medical chart.<br/> RESULTS: The mean age was 80.8 years, and 60.8% of the population were female. Patients were prescribed a mean of 11.3 medications at home. Overall, 636 DRP were detected in the study population. In the adjusted analysis, the difference between the two groups was 2.7 (95% confidence interval 2.0-3.3) DRP detected favoring the group with a pharmacist.<br/> CONCLUSION: The inclusion of a pharmacist in an interdisciplinary team in an ambulatory geriatric-care clinic was associated to a positive impact on care by substantially increasing the number of DRP detected in older patients.