AimMalnutrition is a common geriatric syndrome with multiple negative outcomes including mortality. However, there is a scarcity of literature that focuses on the relationship between malnutrition risk and its clinical implications on geriatric syndromes and mortality among cancer patients. The aim of this study is to determine the clinical importance of malnutrition risk in geriatric oncology practice.Method180 patients with cancer who were ≥ 65 years were included in the study. All patients were questioned in terms of geriatric syndromes, including polypharmacy, frailty, probable sarcopenia, fall risk, dynapenia, depression, cognitive impairment, insomnia, and excessive daytime sleepiness. Mini Nutritional Assessment scores > 23.5 and 17–23.5 were categorized as well-nourished and malnutrition risk, respectively.ResultsOf the 180 patients (mean age 73.0 ± 5.6 years, female: 50%), the prevalence of malnutrition risk was 28.9%. There was no statistically significant difference between the groups in terms of age, gender, education, marital status, body mass index, and comorbidities except for chronic obstructive pulmonary disease (p > 0.05). After adjustment for age, sex, and body mass index; polypharmacy (odds ratio [OR]: 3.17; 95% confidence interval [CI], 1.48–6.81), reduced calf circumference (OR: 3.72; 95% CI, 1.22–11.38), fall risk (OR: 2.72; 95% CI, 1.03–7.23), depression (OR: 6.24; 95% CI, 2.75–14.18), insomnia (OR: 4.89; 95% CI, 2.16–11.05), and frailty (OR: 2.44; 95% CI, 1.75–3.40) were associated with malnutrition risk compared to well-nourished patients (p ConclusionThe risk of malnutrition was associated with a higher risk for all-cause mortality in older patients with cancer, and was associated with many geriatric syndromes, including polypharmacy, fall risk, frailty, insomnia, and depression.</p