Thyroid hemiagenesis is a rare congenital anomaly. Most of the patients diagnosed have an associated thyroidal disease. Ultrasonography (US) is the first radiological choice for diagnosis of thyroidal disease. In this report we described US and scintigraphy findings of a left thyroid lobe hemiagenesis in a female adult and review the literature in relation to this case; discussed the problems associated with this unusual congenital anomaly.