Background: The prevalence of multinodular goiter in all over the world is high, commonly in developing countries. Incidence of differentiated thyroid carcinoma among patients with multinodular goiter is increased in recent literature. Aim of study: To determine the incidence rate of differentiated thyroid carcinoma among patients with multinodular goiter. Patients and methods: This study is a cross sectional study carried out in Surgical Ward of Baghdad Teaching Hospital during the period from 1st of October, 2016 to 31st of September, 2017 on convenient sample of 120 patients with multinodular goiter. Clinical history and examination, fine needle aspiration and postoperative histopathology examination was done to confirm the diagnosis. Results: Mean age of patients was 43.9 years, with 10 males and 110 females. Fine needle aspiration test showed that 26 (21.7%) multinodular goiter patients had differentiated thyroid carcinoma, while 94 (78.3%) patients had benign goiter. The histopathology of multinodular goiter patients revealed that 40.8% of them had colloid goiter, 17.5% of them had micro-papillary carcinoma and 37,5% of them had follicular adenoma. Differentiated thyroid carcinoma among multinodular goiter patients was significantly associated with smoking and exposure to ionizing radiation. Conclusions: The incidence of differentiated thyroid carcinoma among multinodular goiter patients is high. Highlights: