Thyroid hemiagenesis is a rare congenital abnormality in which one of the thyroid lobes is not developed. It can be associated with various thyroid diseases, such as Grave’s disease, nodular goiter and thyroid neoplasm, rarely with hyperparathyroidism. We report a case of a 50-year old woman with left thyroid lobe agenesis diagnosed by ultrasonography and scintigraphy. Right thyroidectomy was performed and the histopathological examination showed diffuse hyperplasia, multinodular goiter and Hashimoto’s thyroiditis. To our knowledge, this is the first description of multinodular goiter and Hashimoto’s thyroiditis in a patient with thyroid hemiagenesis.