Nine children with juvenile chronic myelogenous leukemia (JCML) were diagnosed in an 8-year period from 1977 to 1984. The clinical courses and outcomes of five patients who received minimal or no chemotherapy were compared with that of four patients who were treated with intensive acute nonlymphoblastic leukemia (ANLL) combination chemotherapy. None of the five patients in the former group achieved clinical remission and their survivals were 1, 4, 4, 7, and 29 months, respectively. All four patients in the latter group achieved clinical remissions that lasted 11, 21, 21, and 27 + months, respectively. The durations of their survival (21, 26, 30, and 32 + months) were significantly better than the five patients who received minimal or no chemotherapy (P less than .05). Despite hospitalizations for chemotherapy and for treatment of chemotherapy-associated complications, the clinical status and quality of life of the children who achieved clinical remission were superior to those who remained in relapse. Although intensive chemotherapy induced lengthy remissions, three of the four patients have relapsed. Cytogenetic and cell culture data indicated that the monocytic-macrophage cells characteristic of JCML appeared to be suppressed during remission rather than totally eliminated. We recommend that ANLL-type combination chemotherapy be used as the initial treatment of JCML because of its promptness in effecting clinical remissions. Improved maintenance and consolidation protocols have to be developed to produce durable remissions and cures. Alternatively, bone marrow transplantation may be a useful option soon after remission is achieved with chemotherapy.