Diabetes mellitus and thyroid dysfunction are two major highly-spread health problems worldwide. Both of them affect each other, and the recognition of the relationship between diabetes mellitus and thyroid dysfunction is of importance to guide clinicians in good management of both of them. The present study aimed to find out the prevalence of thyroid dysfunction among diabetic patients in Qurayat Diabetes Center (QDC). Materials and methods:Two hundred (100 type 1 & 100 type 2) diabetic patients were retrospectively investigated who were admitted for the Diabetes Centre in Al Qurayyat Governorate, Al-Jouf, and KSA. Parameters investigated in the study are age, body mass index, fasting bood glucose, post-prandial blood glucose, glycosylated hemoglobin, free triidothyronine (fT3), free thyroxine (fT4) and thyroid-stimulating hormone (TSH). Results:Among the diabetic patients studied, 69% had normal thyroid profile (euthyroid) and 31% showed thyroid dysfunction (25% had subclinical hypothyroidism, 3.5% had clinical hypothyroidism, and 2.5% had clinical hyperthyroidism) while no cases of subclinical hyperthyroidism were found. Conclusion and recommendation:Subclinical hypothyroidism is the most prevalent thyroid dysfunction in our diabetic patients. It increases the risk of cardiovascular complications, and its most important consequence is high possibility of progression to clinical hypothyroidism. It is therefore important to diagnose thyroid dysfunction in diabetic patients to prevent further complications, and this practice should be carried out in clinical settings. Keywords