Background: The recurrent pyogenic infections of patients with hyper-IgM syndrome are controlled by intravenous gamma globulin administration, but patients may suffer from early-onset oral ulcerations and warts. Objective: We have characterized the mucocutaneous manifestations associated with this condition to allow physicians to more readily identify it. Methods: Three male patients with the mucocutaneous manifestations of the hyper-IgM syndrome are described. In one, histopathologic examination of the oral mucosal lesion was performed. Results: Recurrent large, painful oral ulcerations can occur that are not necessarily associated with neutropenia nor do they respond to granulocyte colony-stimulating factor administration. Histopathologic examination of an ulcer showed a heavy infiltrate of mixed inflammatory cells. Warts tend to be widespread and resistant to traditional therapy. Conclusion: Physicians should consider this uncommon condition when examining a male patient with severe oral ulcers or recalcitrant widespread warts. (J Am Acad Dermatol 1998;38:191-6.)