OBJECTIVE: To evaluate sensitivity and specificity of frozen-section biopsy in the diagnosis of acute invasive fungal rhinosinusitis (AIFRS). STUDY DESIGN AND SETTING: Retrospective chart review of all patients treated for AIFRS at the University of Miami between 1993 and 2005. Twenty patients with the clinical diagnosis of AIFRS were identified. Histopathological data were collected to evaluate the use of frozen-section biopsy to diagnose the disease. RESULTS: Permanent pathology sections were positive for AIFRS in all specimens. Frozen-section biopsies were positive for fungal features in all but five cases (four with Mucor and one with Aspergillus). High positive predictive values were found for both fungal types and for both sets of patients (bedside and intraoperative). CONCLUSION: Frozen-section biopsy is a useful tool for rapid and effective diagnosis in patients with suspected AIFRS. A positive frozen-section result is highly predictive of invasive disease and merits prompt surgical intervention.