The etiology and clinical definition of intractable recurrent ulcer of the oral cavity and pharynx were long unknown. Then, intractable recurrent ulcer of the oral cavity and pharynx was defined as irregular ulcerative lesions occurring only in the oral cavity and pharynx, showing no specific findings in clinicohematological examinations, which recurred easily and were resistant to various treatments for at least one month. Twenty-five cases of intractable recurrent ulcer of the oral cavity and pharynx were treated in our hospital. Patient age, sex, chief complaint, past history, duration of illness, the locations and clinical findings of the ulcers, clinico-hematological examinations, the pathology of the ulcers, therapy and prognosis were analysed. Disease specificity was found in age, sex, past history, locations and clinical findings of the ulcers, and prognosis. Our results suggest that intractable recurrent ulcer of the oral cavity and pharynx is a characteristic disease. The possibility that HLA-linked genetic factors play a role in the development of intractable recurrent which ulcers, which in addition to other factors, induce local immunoreaction which then prolongs the course of this disease, was suggested.