OBJECTIVE: Cases of varicella pneumonitis were reviewed to examine the effects of acyclovir therapy on outcome. METHODS: A retrospective chart review was done of all admissions of adults to two hospitals, between 1985 and 1995, because of complications of chickenpox. RESULTS: Fifteen patients were hospitalized for varicella pneumonitis during this period. No patient had a history of chickenpox as a child; all had a recent history (within 2-4 weeks prior to admission) of exposure to chickenpox in their family or neighborhood and developed respiratory symptoms 1 to 4 days after the appearance of the rash. Twelve patients (80%) had a history of cigarette smoking, and seven patients had a platelet count below the normal range. All patients were treated with intravenous acyclovir within 24 hours of admission, and all but one survived and were discharged from the hospital without comorbid conditions. The one mortality was attributed to bacterial superinfection. CONCLUSIONS: Acyclovir treatment may be of benefit for varicella pneumonitis, but no controlled trial has been performed to definitively answer this question.