A 3-hour-old phenotypically normal girl was transferred to Children's Hospital Medical Center because of skin nodules, hepatosplenomegaly, and marked leukocytosis. The predominant cells in the blood, bone marrow, and dermis were monoblasts consistent with congenital leukemia. Known causes of leukemoid reactions were excluded. The infant received two double-volume exchange transfusions but no chemotherapy. As the white blood cell counts decreased, the monocytic cells became more mature, suggesting that the monoblasts had the ability to differentiate. The proliferative capacity of the marrow appeared to be normal as determined by the ability of marrow cells to form colonies in soft agar. Chromosomal analysis of bone marrow blasts including trypsin--Giemsa banding was normal. Three weeks after birth the patient's CBC and physical examination were normal, and the bone marrow was normal by 4 months of age. The patient has remained in remission for over 3 years.