During a 24 mo. period, 34 cases of nosocomial sinusitis associated with nasopharyngeal instrumentation were identified in 32 severely traumatized patients, accounting for 5% of all nosocomial infections. Diagnosis was based on roentgenographic findings consistent with acute sinusitis and either purulent material aspirated from the involved sinus or purulent nasal discharge. All patients had fever and most had leukocytosis. Forty-one pathogens, mostly Gram-negative bacilli, were recovered from 25 patients by aspiration of their sinuses; 14 infections were polymicrobic. Possible predisposing factors were nasotracheal tubes, nasogastric tubes, nasal packing, high-dose corticosteroids, prior antibiotic therapy and facial and cranial fractures. With treatment and removal of the nasal tube, 20 patients had clinical resolution of their disease. Seven, although asymptomatic, had persistent radiological abnormalities consistent with chronic sinusitis. Five patients died of intercurrent disease before resolution of their sinusitis. Sinusitis should be ruled out as a cause of infection in febrile intensive care patients with an indwelling nasal tube.