OBJECTIVE To determine bacterial and fungal organisms that are present in patients undergoing surgery for chronic frontal sinusitis. METHODS Retrospective, nonrandomized study. METHODS Retrospective, nonrandomized bacterial and fungal cultures were performed on 46 sinus aspirates obtained by frontal sinus trephination performed on 30 consecutive patients with chronic frontal sinusitis. RESULTS Six patients were having sinus surgery for the first time, 19 patients had undergone prior functional endoscopic sinus surgery without instrumentation of the frontal sinus/recess, and the third group included 5 patients who had undergone prior frontal sinus/recess surgery. Preoperative computed tomography scan of the frontal sinuses revealed complete opacification in 63% (29/46 frontal sinuses) and partial opacification in 22% (10/46), and no data were available for 15% (7/46). Aerobic cultures revealed that 38% (13/35 cultures) had no growth, 21% (7/35) grew Staphylococcus aureus, 21% (7/35) grew coagulase-negative Staphylococcus, 9% (3/35) grew Haemophilus influenzae, and 26% (9/35) grew a variety of other organisms. Anaerobic cultures were positive in 3% (1/32) of sinuses, and fungal cultures were positive in 4% (1/24). Haemophilus influenzae was most common in primary cases, whereas coagulase-negative Staphylococcus was most common in patients undergoing revision frontal sinus surgery. There were no other significant differences between cultures from patients undergoing revision frontal sinus surgery, revision functional endoscopic sinus surgery without prior frontal surgery, and primary surgery. CONCLUSIONS This study suggests that organisms involved in chronic inflammatory disease of the frontal sinus may change after previous sinus surgery. The study failed to support a significant role for anaerobes. The role for coagulase-negative Staphylococcus as a potential pathogen or a contaminating agent remains unclear.