Juvenile myelomonocytic leukemia (JMML) is the most common myeloproliferative/myelodysplastic disorder seen in children. The treatment of choice, allogeneic stem cell transplantation, provides the only known cure for the disease, but relapse after transplant is common. The authors describe a 5-year-old boy diagnosed at age 34 months with JMML that evolved to acute myeloid leukemia. Initial treatment consisted of fludarabine and cis-retinoic acid therapy, followed by a matched sibling bone marrow transplant. After a relapse, he received a second transplant from the same donor, using peripheral blood stem cells, followed by repeated donor leukocyte infusions. After the second relapse, he received the farnesyltransferase inhibitor R115777 (tipifarnib, Zarnestra), but the leukemia persisted. When bone marrow blasts numbered 60% of the mononuclear cells, he received single-agent clofarabine induction (52 mg/m2/d) for 5 days. After three courses, he attained a remission marrow with 5% blasts and disappearance of the 5q- and 9q-cytogenetic abnormalities. Copyright © 2005 by Lippincott Williams & Wilkins.