Background: Geriatric assessments and interventions improve the outcomes of hospitalized older adults with cancer, but their implementation in developing countries is limited. We studied the effect of a specialized geriatrician-led inpatient geriatric management unit compared with a conventional internal medicine ward on the outcomes of hospitalized Mexican older adults with cancer. Methods: This retrospective study included patients aged ≥65 with solid tumors who had a cancer-related hospitalization at a public academic center in Mexico City between March 2015 and October 2018. Patients hospitalized in the geriatric management unit (cases) were paired in a 1:2 fashion with those in internal medicine wards (controls). Pairing was done by age (+/- 5 years), tumor type, and admission date (+/- 3 months). We studied the effect of being hospitalized in the geriatric management unit on length of stay (LOS), incidence of delirium, hospital-acquired complications, and in-hospital mortality. Multivariate logistic regression models for each outcome were created using variables which were significant on univariate analysis. Results: 300 patients (100 cases, 200 controls, median age 75) were included. The most common tumors were gastrointestinal (GI) (53%) and genitourinary (25%). Both groups were comparable regarding baseline comorbidities (Charlson index 8.5 vs. 7.7, p = 0.99) and illness severity at admission (NEWS2 score 2.6 vs. 2.3, p = 0.82). No difference in median LOS was found between cases and controls (9.1 vs. 9.5 days, p = 0.34). Diagnosis of a GI tumor (OR 3.4, 95% CI 1.3-5.5), hospital-acquired complications (OR 4.9, 95% CI 2.5-7.3), and delirium (OR 5.5, 95% CI 2.3-8.7) were associated with longer LOS. 14% of patients in both groups had delirium. Hospitalization in the geriatric management unit reduced the risk of delirium (OR 0.35, 95% CI 0.1-0.9), while a higher Charlson index (OR 1.2, 95% CI 1.0-1.4), NEWS2 score (OR 1.2, 95% CI 1.1-1.4), and hospital-acquired complications (OR 7.3, 95% CI 2.9-18.5) increased it. 34% of patients developed hospital-acquired complications. Diagnosis of a GI tumor (OR 1.9, 95% CI 1.1-3.3) and higher NEWS2 score (OR 1.2, 95% CI 1.1-1.4) increased the risk of hospital-acquired complications. No differences in in-hospital mortality were seen between cases and controls (12% vs. 10%, p = 0.59). A higher NEWS2 score at admission (OR 1.4, 95% CI 1.2-1.7) and delirium (OR 10.7, 95% CI 3.2-36.3) increased the risk of death. Conclusions: Among older Mexican adults hospitalized for a cancer-related diagnosis, receiving care in a geriatric management unit led to a significant decrease in the risk of delirium. No improvements were seen in LOS, complications, or in-hospital mortality, which were associated with tumor and patient-related characteristics. Geriatric co-management can lead to improved geriatric outcomes in developing countries with limited resources.