Acute sinusitis is a frequent complication in ventilated intensive care patients and may be a possible source of pneumonia or septicemia. A study of 49 ventilated intensive care neurosurgical patients without previously known disease of the paranasal sinuses or midface fractures was conducted retrospectively from 1989-1990. The kind of intubation used (naso- or orotracheal) was taken into account and the period of ventilation examined in order to determine the genesis of inflammatory changes in the paranasal sinuses (as defined by computed tomography). Intensive care patients suffering from sinusitis showed a characteristic early opacity of the sphenoid sinuses, with lesser involvements in the ethmoid and maxillary sinuses. Only in rare cases and after very long periods of ventilation were the frontal sinuses found to be opaque. Nasotracheal ventilation was observed to produce an earlier attack on the intubated ipsilateral sinuses. These findings indicate that nasotracheal intubation should be avoided if possible or the method of intubation changed as early as feasible. If conservative-measures fail sinusitis should best be treated by means of endonasal microsurgical open sinostomy.