Varicella vaccine has shown its efficacy to prevent the disease and complications in healthy and immunodeficient children. In this article the authors evaluate the immunologic status of acute lymphoblastic leukaemia at diagnosis and at follow up and the development of chickenpox and/or herpes zoster. Children with negative serology and continuous complete remission of acute lymphoblastic leukaemia for one year were vaccinated. Of 71 children diagnosed of acute lymphoblastic leukaemia from 1983 to 1996, 25 received the vaccine and seroconversion was obtained in 76% after one dose and 92% after the second dose. Vaccine tolerance was adequate. The incidence of herpes zoster infection was decreased in vaccinated children during chemotherapy compared to the wild-virus infected ones. Nowadays that vaccine for healthy children is recommended, we consider a priority to protect from chickenpox the children affected by leukaemia that are in continuous complete remission of the disease.