To determine the clinical features, treatment and outcome of severe varicella pneumonia with hypoxic respiratory failure requiring intensive care management, a prospective survey of consecutive cases was undertaken. Fifteen consecutive adult cases of varicella pneumonia with respiratory failure admitted to a 10-bed respiratory intensive care unit over a period of 10 y from 1984-1993 were studied. All patients were given acyclovir immediately on admission. The level of ventilatory support needed was determined by the severity of gas exchange abnormality, and varied from face mask oxygen (three patients), through continuous positive airway pressure (CPAP) by face mask (eight patients), to continuous positive pressure ventilation (CPPV) (four patients). The majority of patients were young females, only one of whom was pregnant. All patients had been in close contact with a known case of chickenpox. All patients responded well to acyclovir and ventilatory support with improved oxygenation. Monitoring with pulse oximetry was important to detect episodes of desaturation on inadvertent discontinuation of positive and expiratory pressure (PEEP). Two patients were admitted with bacterial superinfection, and one patient, who had required intubation and CPPV, developed nosocomial respiratory tract infection. There were no deaths. This experience suggests that intensive care admission, with the early administration of intravenous acyclovir and recognition of the severity of the hypoxaemia resulting from varicella pneumonia (which can be reversed with PEEP), should reduce the mortality of severe varicella pneumonia in adults.