Background: Head and neck cancers are considered the 6th most common cancer worldwide. For patients with advanced disease, combined modality treatment including chemo-radiation (CRT) as first-line treatment had improved outcomes for patients with locally advanced disease. The association between radiation exposure and the occurrence of thyroid cancer has been well documented, and the two main risk factors for the development of thyroid cancer are the radiation dose delivered to the thyroid gland and the age at exposure. The risk increases after exposure to a mean dose of more than 0.05-0.1 Gy (50-100 mGy. Nurses' role is not only in the maintenance of the treatment and its adverse effects, but also to act as information disseminators about the disease and its treatment, offering relief measures and helping the patients to cope with the disease Aim: Assess factors affecting thyroid dysfunction in patients with head and neck cancer receiving radiation or chemo-radiation therapy. Design: A descriptive research design was utilized for this study  to meet the aim of the present study. Setting: chemotherapy and radiology units of the Main University Hospital and Charity Ayadi Almostakbl center for cancer treatment in Alexandria.. Subjects: A convenience sample of 100 adult male and female patients. Study tools: Three tools were used. Tool (I) A socio-demographic and clinical data interview schedule, Tool (II) Assessment of head and neck cancer patient's knowledge and Tool (III) Assessment of chemo-radiation side effects on thyroid gland structured interview schedule. Results: The current study showed that  there was statistical significant difference between socio – demographic characteristics and clinical data  and patients overall  Knowledge score and all over sign and symptoms.. Conclusion: The provision of effective education was found to have a profound impact on improving patients' knowledge and practice. Recommendations:    Regular testing of thyroid function in patients undergoing radiation or chemo radiation can help in diagnosing thyroid dysfunction at the subclinical stage, before it progresses to clinical hypothyroidism. Larger multi-institutional studies with longer follow-up are needed to study the morbidity associated with post radiation thyroid dysfunction further.