A 54-year-old man was admitted to Kitano Hospital because of nuchal pain in November, 1984. The bone marrow was hypercellular with 18% of myeloblasts and 45% of erythroblasts many of which were megaloblastoid and positive for PAS-staining. BH-AC . DMP therapy induced a complete remission which was maintained for more than 3 years until April, 1988, when gingival swelling occurred. A biopsy of the gingiva revealed a diffuse infiltration of myeloblasts together with a few erythroblasts. Local irradiation resulted in he disappearance of the swelling. However, the microscopic infiltration of the leukemic cells in the gingiva still remained in December, 1988 when there was no apparent gingival swelling and the patient was in a second hematological remission. Bone marrow relapse occurred in September, 1988 and twice thereafter. Complete remissions were again achieved for the first two relapses and the leukemic infiltration of the gingiva disappeared after another irradiation. The third relapse was refractory to an intensive chemotherapy and the gingival swelling also recurred in July, 1989. The patient died of pneumonia in October, 1989. The gingiva may be more common site of extramedullary relapse. Careful observation of this organ would be necessary throughout the course of leukemias.