Thyroidal hemiagenesis resulting from the failure of development of one thyroidal bud to develop accounts for fewer than 0.1% of thyroidal disorders necessitating surgery. This rare congenital anomaly usually occurs on the left side. Any nonfunctional lobe detected by scintigraphy needs to be evaluated further by ultrasonography, because thyroid hemiagenesis is associated with varying degrees of morbidity when it coexists with other anomalies requiring surgical intervention. We report the case of a 38-year-old woman with preoperatively diagnosed thyroidal hemiagenesis, who underwent surgery in our clinic. We review the literature in relation to this case, and discuss the problems and complications associated with this unusual congenital anomaly.