Introduction: Diabetes Mellitus (DM) lead to multiples complications. We hypothesize that chemotherapy-related adverse events (AEs) could be increased in diabetic patients. Main objective: to compare the occurrence of severe AEs corresponding to grade 3/4 AEs within 90 days following the onset of the chemotherapy between diabetic and non-diabetic patients. Methods: A retrospective monocentric study in Lille University Hospital Oncology Unit. Inclusion criteria: patients treated for a first cycle of chemotherapy between May 2013 and May 2016. Exclusion criteria: patients with an history of cancer whatever the treatment carried out. Results: 609 patients were included, 490 (80.5%) non-diabetics and 119 (19.5%) diabetics (Figure 1). After multivariate adjustement on age at cancer diagnosis, sex, general status, type of cancer, type of chemotherapy, presence of metastases and denutrition, diabetics had an increased risk of G3/4 AEs within 90 days compared to non-diabetics patients (multivariate OR: 1,57 [1,02;2,42], p=0,04) (Table 3). More frequent AEs were infection (26%), haemotological toxicity (13%), endocrinological toxicity (13%) including hyperglycemia. Conclusion: Diabetes mellitus lead to an increased risk of G3/4 AE occuring early after the beginning of the chemotherapy. A better consideration of its impact by oncologists is warranted.