Seven children, 11 months to 5.9 years of age, with juvenile myelomonocytic leukaemia (JMML) underwent allogeneic haemopoietic cell transplantation (HCT) using related or unrelated donor bone marrow or umbilical cord blood. All patients had active disease at time of transplant despite chemotherapy in five patients and chemotherapy and splenectomy in one patient prior to HCT conditioning. All patients received cyclophosphamide and TBI, with the addition of busulphan in two cases. Engraftment was documented in all cases. Notably, six of seven patients relapsed after allogeneic HCT with one achieving a return to full donor chimaerism after cyclosporin A (CSA) withdrawal. Two patients are alive in remission, 23+ and 30+ months after transplant. The role of allogeneic HCT in patients with JMML is discussed. A cooperative multicentre trial is needed to establish the optimal therapy for these patients.