Background: Iodine is a necessary element of the hormones produced by the thyroid gland. Basically, thyroglobulin (Tg), a thyroid-specific protein, that reflects the size of the thyroid gland, is usually considered a biomarker of urinary iodine status of several patients. But in Bangladesh, we do have not enough information regarding the sensitivity, specificity, and predictive value of thyroglobulin in determining iodine deficiency among simple diffuse goiter patients. Aim of the study: The aim of this study was to evaluate the sensitivity, specificity, and predictive values of thyroglobulin in determining iodine deficiency among simple diffuse goiter patients. Methods: This cross-sectional observational study was conducted at the Department of Endocrinology, Bangabandhu Sheikh Mujib Medical University (BSMMU), and Dhaka Bangladesh. The study was conducted during the period from May 2014 to March 2016. The targeted sample size of this study was between 39 and 90 and the final sample size was finalized as 87. A purposive sampling technique was used to select 87 patients with simple diffuse goiter attending the outpatient department of the mentioned hospital. Results: In this study, we did not find any statistically significant difference in urinary iodine between the different cut-off values of serum thyroglobulin at 14.46 (ng/ml). Similarly, there was not any statistically significant difference in urinary iodine levels at different cut-off values of thyroglobulin. Thyroglobulin had a high negative predictive value and comparatively low positive predictive value in determining iodine deficiency, at 98.51% and 30% respectively. Serum thyroglobulin had 85.71% sensitivity and 82.50% specificity. Thyroglobulin also had a high negative predictive value at 98.51%, but a low positive predictive value at 30%. The overall accuracy of thyroglobulin as an indicator for iodine deficiency was 82.76%. Conclusion: Thyroglobulin seems to have an inverse association in iodine deficiency state and a positive association in over sufficient state with UI. The overall sensitivity of thyroglobulin was satisfactory but the specificity was found very low. Considering the urinary iodine as the gold standard, basically, the positive predictive value of thyroglobulin was found very low but the negative predictive value was found very high.