Background: Chemotherapy toxicity (CT) is higher in elderly cancer patients, mainly due to fragilities identified in this subgroup. Hospitalization can be an adverse outcome of cancer treatment, which is disruptive in older patients, leading to worse functional status and cognitive disfunction, as well as increased costs for the health system. We evaluated patients treated with chemotherapy to identify hospitalizations related to oncological treatment and factors associated with this outcome. Methods: A retrospective study was conducted in a Brazilian Oncology Center. Patients ≥65 years old who started chemotherapy for solid tumors as curative or first-line therapy in 2019 were included and data was collected of the entire treatment until suspension or change in therapy (because of progression, completion, toxicity, or death). Those treated concomitantly with immunotherapy and radiotherapy were excluded. Characteristics of patients and their treatments were analyzed as risk factors for hospitalization through univariate analysis (UVA) with Fisher’s Exact Test and Mann-Whitney Test, and those variables considered significant (p < 0.05) were submitted to a multivariate analysis (MVA) with Logistic Regression. Results: We included 124 patients with a median of 70 (65-93) years old and a median of 6 (1-26) cycles of chemotherapy completed. There were 67% of women, 42.8% had Charlson Comorbidity Index (CCI) ≥1; polypharmacy (≥5 medications) was present in 38.7%; the main cancer treated were gastrointestinal (34.7%), breast (21%) and pancreas/biliary tract (20.2%). Most patients had metastatic disease (54%) and received polychemotherapy (80.6%) as primary treatment ;body index measure was ≥25 in 50.8% and 24.2% lost 5% or more of body weight during the time analyzed. Unplanned hospitalizations occurred in 40 patients and 25 were considered associated with CT (febrile neutropenia, infections, gastrointestinal adverse events, worse renal function). In UVA, age, pancreas/ biliary tract cancers, CCI≥1 and polypharmacy were factors associated to hospitalization due to CT. After MVA, only CCI≥1 (OR 3.23, CI95%1.12 – 10.05) continued as an independent factor associated to CT. Conclusions: Evaluation of comorbidities with CCI can identify older patients at higher risk of hospitalization due to toxicity during treatment with chemotherapy. Comprehensive geriatric assessment should be offered to high-risk patients in order to develop strategies to prevent this adverse outcome.