This paper reports a relapsed case of acute myeloid leukemia with intracranial, testicular and intestinal tumor formation. A-56-year-old male, diagnosed as M1 on September, 1988, entered complete remission on October 14, 1988, aided by JAL-SG and AML-85 regimen. Blast cells with Auer rods demonstrated 8;21 translocation lacking 11q with 30 of 30 analyzed bone marrow cells, and the following antigen pattern: CD5+, CD19+, CD33+, CD56+, HLA-DR+. After 4 courses of post remission therapy, the maintenance therapy was discontinued because of his liver dysfunction. He was discharged on May, 1989, and was seen as an out patient. He complained of left hemiplegia and was re-admitted on September 30, 1989. Though the bone marrow was in complete remission on September 4th, CT scan and MRI demonstrated intracranial tumor formation. Bone marrow relapse occurred on October 27th, eventually resulting in his death on November 18th. Autopsy showed intracranial, testicular and intestinal tumor formation and blast cell invasion into the liver, spleen and kidneys. We analyzed the characteristics of 14 cases with intracranial tumor formation previously reported. The focal neurological symptoms reflecting the intracranial tumor mass effect were considered to be important initial signs. CT scan was a useful tool for diagnosis. The average age of the 14 cases was 38, 9 and the male/female ratio was 9:5. Six of 9 cases, diagnosed by FAB classification, were M2 and one of the 6 cases in whom chromosomes of blast cells were examined had t(8;21). Though irradiation seemed effective for the reduction of tumor mass, the patients' prognosis was poor.(ABSTRACT TRUNCATED AT 250 WORDS)