BACKGROUND: Expert groups have recommended incorporation of a geriatric assessment into clinical practice for older patients starting oncologic therapy. However, that practice is not standard primarily because of resource limitations. In the present study, we evaluated the effect on treatment decisions by oncologists in the community oncology setting of a brief geriatric assessment tool that estimates risk of toxicity. METHODS: This prospective longitudinal study in 5 community oncology practices in British Columbia involved patients 70 years of age and older starting a new cytotoxic chemotherapy regimen. Clinical personnel completed a brief validated geriatric assessment tool-the Cancer and Aging Research Group chemotherapy toxicity tool (carg-tt)-that estimates the risk of grade 3 or greater toxicity in older patients. Physicians were asked if the carg-tt changed their treatment plan or prompted extra supports. Patients were followed to assess the incidence of toxicity during treatment. RESULTS: The study enrolled 199 patients between July 2016 and February 2018. Mean age was 77 years. Treatment was palliative in 61.4% of the group. Compared with physician judgment, the carg-tt predicted higher rates of toxicity. In 5 patients, treatment was changed based on the carg-tt. In 38.5% of the patients, data from the tool prompted extra supports. Within the first 3 cycles of treatment, 21.3% of patients had experienced grade 3 or greater toxicity. CONCLUSIONS: This study demonstrates that use of a brief geriatric assessment tool is possible in a broad community oncology practice. The tool modified the oncologist's supportive care plan for a significant number of older patients undertaking cytotoxic chemotherapy.