During the period July 1986 through December 1991, 67 children were treated for non-B-cell acute lymphoblastic leukemia at The Juliane Marie Centre, GGK, The University Hospital Rigshospitalet, Copenhagen. Twenty-five children were susceptible to varicella zoster (VZ) virus at diagnosis. For these patients the cumulated risk of VZ exposure was 90% after 32 months. Five patients developed varicella (two of whom had pneumonitis) during the period of antileukemic treatment. Two of these had received prophylactic treatment with acyclovir. The 2 year cumulated risk of having chickenpox or herpes zoster in children with previous VZ infection was 24% and 34%, respectively. VZ vaccination ought to be considered for this group of children in order to diminish transmission and morbidity.