Central nervous system vasculitis after chickenpox--cause or coincidence? A 7.5 year old boy, known to have a seizure disorder, presented with an infarct in the left middle cerebral artery territory, 10 weeks after severe chickenpox. Immunofluorescent antibody titre to the varicella zoster virus in the cerebrospinal fluid was 1:32. Cerebral angiography showed evidence of focal vasculitis. He presented again seven months later with an acute exacerbation of seizures. Magnetic resonance imaging of the brain showed an old posterior extension of the infarct, but a repeated angiography demonstrated an improvement in the vasculitic process. Cerebrospinal fluid antibody titre was again 1:32. Although this may have been an unfortunate coincidence, a possible association between chickenpox and vasculitis, similar to that reported with herpes zoster, and with potentially significant clinical implications, should be considered. As a definite proof can be obtained only by a brain biopsy, however, which is generally not indicated in such cases, only additional clinical reports can lead to delineation of this association as a definite entity. 