Background Malnutrition is frequent in older cancer patients, with a prevalence that ranges from 25% to 85%. The aging process is associated with several physiological changes, which may have implications for nutritional status. Screening tools can be useful for identifying malnutrition status among older patients with cancer. Methods A hospital-based multicenter cohort study that included 44 institutions in Brazil. The Mini Nutritional Assessment-Short Form (MNA-SF) was administered to 3061 older hospitalized cancer patients within 48 hoursof admission. The Kolmogorov-Smirnov test was used to test the sample distribution, considering sex, age range, calf circumference, body mass index, and MNA-SF score and classification. The categorical data were expressed by frequencies (n) and percentages (%)and compared using the chi-square test or Tukey test. Results According to the results of the MNA-SF, 33.4% of the patients were malnourished, 39.3% were at risk of malnutrition, and 27.3% were classified as having normal nutritional status. Length of hospital stay (in days) was found to be longer for those patients with a poorer nutritional status (malnourished: 7.07±7.58; at risk of malnutrition: 5.45±10.73; normal status: 3.9±5,84; p <0.001). Conclusions The prevalence of malnutrition and nutritional risk is high in older hospitalized cancer patients in all the regions of Brazil and a worse nutritional status is associated with a longer hospital stay. Using a low-cost, effective nutritional screening tool for older cancer patients will enable specialized nutritional interventions and avoid inequities in the quality of cancer care worldwide.