Background: Although some clues exist about the causative relationship of fungi and chronic rhinosinusitis, the relationship of nasal polyps and fungi has not been enlightened. The purpose of this study was to determine whether a relationship exists between fungi and massive nasal polyps and to evaluate current available diagnostic techniques for detection of fungi. Methods: Thirty cases of massive nasal polyposis (NP) were evaluated prospectively for fungal evidence and were compared with 18 cases of concha bullosa based on direct microscopy, fungal culture, serology, polymerase chain reaction (PCR), and sequencing. Results: Fungal colonization was detected in 15 (50.0%) of the cases with massive NP, but only in 2 (11.1%) of the cases with concha bullosa. A significant difference was found between the study and the control groups in terms of fungal existence (p < 0.016). Direct microscopy was positive in 14 (46.7%) and 1 (5.6%) of the cases; fungal culture was positive in 8 (26.7%) and 4 (22.2%) of the cases; serology was positive in 9 (30.0%) and 2 (11.1%) of the cases; PCR was positive in 18 (60.0%) and 6 (33.3%) of the cases with massive NP and concha bullosa, respectively. Conclusion: Fungal colonization was found to be more common in massive NP patients compared with the control group. According to our results, microscopy and PCR were most sensitive techniques for detection of fungi. Copyright © 2007, OceanSide Publications, Inc.