Thyroid hemiagenesis is a very rare congenital anomaly in which one thyroid lobe fails to develop. The cause of thyroid hemiagenesis is still unknown. The true prevalence of thyroid hemiagenesis is not known, but it is estimated to be from 0.05% to 0.2% in normal children. Thyroid hemiagenesis is common in female with the left lobe being absent. The common disease in the remaining lobe is hyperthyroidism, benign adenoma, a toxic multinodular goiter, chronic thyroiditis, primary myxedema, and rarely carcinoma. Tc-99m pertechnate scintigraphy, ultrasonography and computerized tomography can be used to confirm this anomaly. Here we report three cases with left lobe agenesis. Two of them were euthyroid state while the other hypothyroid patient had a ectopic lingual thyroid.