The case is described of a boy who presented at age six months with symptoms and signs of a thyroglossal cyst, which seemed to be confirmed by ultrasound findings. The cyst slowly increased in size, and eventually the patient underwent Sistrunk’s procedure at age four years. Histology showed that the cyst was in fact a mixed thyroglossal and dermoid cyst. This casts doubt on the doctrine that thyroglossal cysts and dermoid cysts are anatomically and histologically separate entities, and strengthens the view that these cysts should be more appropriately named ’thyroglossal abnormalities’.