Rhinosinusitis is a common complication in patients with nasopharyngeal carcinoma (NPC) who receive radiotherapy. An impaired mucociliary clearance due to this treatment may be the major cause of rhinosinusitis in these irradiated patients. The relative frequency with which various pathogens cause rhinosinusitis in these patients is unknown. This study investigates the bacteriology of acute rhinosinusitis in irradiated NPC patients by maxillary sinus puncture. From October 2001 through July 2006, 20 irradiated NPC patients with radiograph-proven acute maxillary sinusitis received maxillary sinus punctures. Aspirate contents of the sinuses were collected for aerobic and anaerobic cultivation. A total sampling of 26 sides was performed in the 20 patients. The culture rate was 85%. Frequently identified aerobes and facultative anaerobes included alpha-hemolytic streptococcus (n = 8), Staphylococcus aureus (n = 5) and Pseudomonas aeruginosa (n = 3). Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, however, are far less common. This may provide important information about the antibiotic therapy in irradiated NPC patients with acute rhinosinusitis.