The hypereosinophilic syndrome is a multisystem disease characterized by infiltration of eosinophils in bone marrow, heart, and other organs. Cutaneous involvement occurs, but usually it appears late in the disease and is of less importance than the cardiac and other organ involvement. We describe two patients with the hypereosinophilic syndrome (HES) in whom the initial manifestations of the disease were recurrent, severe mucosal ulcers involving the mouth and genitalia. In both patients, the mucosal involvement antedated the cardiac manifestations of the disease, and in both, the disease was refractory to treatment.