Aleukemic leukemia cutis is a rare form of leukemia manifestation, defined as a skin infiltration of leukemic cells with no evidence of leukemia in the bone marrow. A 4-month-old girl was referred to our hospital because of exanthema that appeared and regressed repeatedly. Histological examination revealed partial infiltration of histiocytic cells in the skin lesion. However, the diagnosis could not be made at that time. At 9 and at 13 months old, appearances of exanthema similar to the previous time were combined with systemic fever, abnormal coagulation tests, and the marked increases of atypical lymphocytes in peripheral blood: however, these symptoms resolved spontaneously. At 14 months old, deterioration of the exanthema and an increase in the peripheral leukocyte counts were observed. Bone marrow aspiration revealed the predominance of monocytic blasts (76.4%), and the patient was diagnosed as having acute monocytic leukemia (M5b) with leukemia cutis. Complete remission was obtained with standard chemotherapy. Six months after the therapy was completed, an extramedullary relapse occurred in the inguinal lymph nodes, which was successfully treated with allogeneic bone marrow transplantation from an HLA-matched unrelated donor, and the patient has been free of disease for two years after the transplantation.