Objective: To evaluate the use of maxillary sinus puncture as a routine diagnostic procedure to exclude or confirm purulent sinusitis in intensive care unit (ICU) patients presenting with fever or a septic state of unknown origin. Study Design: Retrospective. Methods: All patients admitted to the ICU at the University Hospital Ghent who required ENT examination to exclude acute sinusitis as possible cause of their otherwise inexplicable fever or septic state underwent maxillary sinus puncture via the inferior meatus. The results of clinical examination and the relation between the presence of foreign bodies (e.g., nasogastric tubes) and culture results from the middle meatus and sinuses were analyzed. Results: One hundred five punctures were performed in 53 patients. Macroscopic purulent effusions were obtained from 25 and nonpurulent effusions from 19 sinuses. The presence of a nasogastric tube did not influence puncture results but significantly increased colonization of the middle meatus. Staphylococcus aureus and Gram-negative agents were frequently cultured from sinus aspirates. Although purulent secretions often reveal no growth, most patients present with a multibacterial (40%) or monobacterial (28%) infection. Simple anterior rhinoscopy reduces the need for antral puncture. Only 8% of punctures in patients with a normal clinical examination were positive. Conclusions: Antral puncture proves to be a simple, fast, safe, inexpensive, and effective procedure for immediate diagnosis of acute nosocomial sinusitis in ICU patients and is therefore recommended as first procedure in these patients, even when only minor clinical abnormalities are present.