Background/Aim: No studies have examined the association between the Geriatric Nutritional Risk Index (GNRI) at the initiation of chemotherapy for malignant lymphoma and the occurrence of adverse events. Therefore, we investigated the impact of GNRI at treatment initiation on the occurrence of side effects and time to treatment failure (TTF) in patients with malignant lymphoma undergoing initial rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) therapy. Patients and Methods: This study included 131 patients who underwent initial R-CHOP therapy between March 2016 and October 2021. Patients were stratified into those with high (GNRI ≥92; n=56) or low (GNRI <92; n=75) GNRI status. Results: Comparing the High GNRI group and Low GNRI group, the incidence of febrile neutropenia (FN) and Grade ≥3 creatinine increase, alkaline phosphatase (ALP) increase, albumin decrease, hemoglobin decrease, neutropenia, and thrombocytopenia were significantly higher in the Low GNRI group. TTF in the High GNRI group was significantly longer than that in the Low GNRI group (p=0.045). Multivariate analysis showed that the factors influencing the duration of treatment were PS (≥2) at the start of treatment, serum albumin level, and GNRI. Conclusion: In patients undergoing R-CHOP therapy, GNRI <92 at regimen initiation increased the risks of developing FN and hematologic toxicity. Multivariate analysis revealed that performance status, albumin levels, and GNRI at regimen initiation were the factors influencing treatment duration. Nutritional status at treatment initiation may influence the development of hematologic toxicity and TTF.Malignant lymphomas are histologically classified into Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), and many patients in Japan have NHL. The male-to-female ratio is 3:2, with a peak incidence at the age between 70-80 years (1). Diffuse large B-cell lymphoma (DLBCL) accounts for more than 30% of all NHL cases in Japan (2). Rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) therapy is the first-line treatment of choice for DLBCL. In addition to hematologic toxicity, R-CHOP is highly emetogenic risk (3); therefore, patients are prone to nausea, vomiting, and anorexia, and 50%, 89%, 24%, and 19% of patients experience nausea and vomiting, leukopenia, thrombocytopenia, and anemia, respectively (4). Furthermore, nutritional disorders and weight loss occur in patients with malignant lymphoma undergoing cancer chemotherapy (5, 6), suggesting poor nutritional status and weight loss due to decreased food intake are associated with adverse events. Weight loss prior to the initiation of cancer chemotherapy is associated with a lower median survival (5) and nutritional status before and during treatment is associated with resistance to treatment, incidence of adverse events, and poor prognosis (5-7). Therefore, the nutritional status of patients undergoing chemotherapy must be assessed to ensure the safety and continuity of treatment, maintain the qual...