A study was undertaken to determine whether children immunized with live varicella vaccine are at greater risk of acquiring herpes zoster than children who have had varicella. Children with acute lymphocytic leukemia who had had varicella were compared with those who received live varicella vaccine. During the period of observation, 15 of 73 children who had varicella acquired herpes zoster and none of the 34 children who had been vaccinated. If the time of observation was adjusted for and the vaccinees who failed to have a sustained antibody response or who acquired chickenpox were removed, the risk of herpes zoster was still less in vaccinees (P = .0075). Because herpes zoster is common in children with acute lymphocytic leukemia, differences in the two groups could be discerned more readily than if normal children were compared. There is no reason to suspect that recipients of live varicella vaccine would be more likely to acquire herpes zoster than children who get varicella.