Diabetes mellitus is often associated with a risk of developing some types of cancer. The association between head and neck cancers and diabetes as well as prognosis and treatment tolerance remains a controversy. Acute toxicities associated with treatment may be amplifi ed by the presence of comorbidities, including hypertension, diabetes and collagen diseases. Another factor implicated in the treatment tolerance is also the limitation by the presence of hyperglycemia of the corticosteroids dose used for the control of pain and edema associated with chemo-irradiation and for the treatment of thrombocytopenia. The purpose of the study was to evaluate the involvement of diabetes mellitus in the toxicities associated with chemo-radiotherapy treatment in multimodal treated patients for advanced local head and neck cancers. For patients with locally advanced non-metastatic head and neck treated with multimodal (chemo-radiotherapy) acute toxicities (radio-dermitis, radio-mucositis, dysphagia) was analyzed comparatively in patients who associate or not cancer with diabetes. It was also compared if the diagnostic of diabetes influenced the intensity of chemotherapy. Identifying the predictive value of diabetes mellitus for the severity of toxicities in multimodal curative treatment for head and neck cancers can lead to limitation of radiation dose to some radiosensitive anatomical structures in the context of the modern IMRT and VMAT irradiation techniques implementation in clinical practice.