Thyroid Disorders in Diabetic Patients. Objective: To evaluate thyroid function and morphology in all diabetic outpatients from our institution. Methods: From 1996 to 1998, all diabetic patients were submitted to thyroid ultrasonography (US) and serum measurement of free T 4 , TSH, TPOAB, and TRAb. The control group, encompassing outpatients of the same hospital without diabetes and thyroid diseases, was submitted to the same evaluation. A patient was shown to have thyroid disorder when two or more measurements were altered, or when the US was abnormal. Results: The diabetic patients (n= 256) differed from controls (n= 75) by presenting a greater frequency of thyroid disorders (51.6% vs. 38.7%; P<0.05). In patients with thyroid disorders, both groups did not differ regarding thyroid function. In diabetic patients with thyroid disorders there was a higher frequency of women, type 2 diabetes, and family history of thyroid disorders. Conclusions: The high prevalence of thyroid disorders in the diabetic population leads us to recommend thyroid evaluations in all diabetic patients.