Objectives: To determine the sensitivity and the selectivity of thyroid ultrasound in diagnosing cancer in multinodular goiter. Patients and methods: A retrospective cohort study composing 2 groups of multinodular goiter patients, 1 benign and 1 malignant (based on postoperative pathological results), collected at random in University Medical Center of Ho Chi Minh city from 2003 to 2008.Results: There were 146 patients (73 patients in each group) with 196 nodules in total.