Abstract: Background: Diabetes mellitus (DM) and Thyroid dysfunction (TD) are the most commonly encountered endocrine disorders which also tend to co-exist. Diabetic patients are more likely to develop thyroid dysfunction than the general population and hence a higher TD prevalence in the population. The prevalence of TD in diabetic patients vary considerably worldwide and is reported between 10-15% with a Meta-analysis reporting an average prevalence of 11% whereas in the general population it ranges between 0.6% to 6%. Similarly studies from Africa have reported varied TD prevalence in DM ranging from as low as 1.6% in South Africa to as high 61% in Kenya. The effect of TD in diabetic patients includes poor glycemic control, precipitation of ketoacidosis and hypoglycemia and amplification of cardiovascular risks. Additionally, insulin resistance, serum lipid derangements and metabolic syndrome profile have also been observed in diabetic patients with TD. Objectives: To determine the prevalence, patterns and predictors of TD in diabetic patients attending diabetic outpatient clinic at Bugando Medical Centre (BMC) Mwanza Tanzania. Methodology: Hospital based cross-sectional study, conducted at the Bugando Medical Centre DM outpatient clinic. A structured pre-tested questionnaire was used to obtain socio demographic and clinical information; files were reviewed to obtain records of previous admissions if present, medications and random of fasting blood glucose levels (records and/or tested on clinic day). Laboratory testing for thyroid hormones (FT3, FT4, and TSH), triglycerides and HbA 1c was done. Results: We evaluated 201 adult diabetic outpatients for thyroid dysfunction, majority of which were female 63.7%, with a median age of 57[47 – 63] years and a median DM duration of 6.5 years. TD was recorded in 64(31.2%) with isolated FT3 thyrotoxicosis being the most prevalent pattern by 47% followed by euthyroid sick syndrome by 28.7% and 29% in TSDM and TIDM respectively was recorded in a sub analysis, with OR [95% CI] of 0.94[0.36-2.34] p value 0.895. Gender and previous history of thyroid disease predicted TD in this population. Clinical symptoms or signs of TD were reported in less than 6% of the study population. Conclusion: The high prevalence of TD in our asymptomatic diabetic out-patients calls for a regular screening and close follow up of our patients. Further studies are warranted to ascertain the impact of treatment of TD in DM population and to further understand long dynamics of TD in DM and in general population.