Acute fungal sinusitis is a life-threatening infection affecting immunocompromised patients. Historically, the most commonly recovered fungi are Aspergillus and Mucor. The extent of potentially disfiguring debridement surgery is grossly determined by the appearance of bleeding at the margins, signifying viable tissue and the absence of fungus. Requests for frozen section may concern the initial diagnosis and the intraoperative verification of margin status. In 12 patients with acute fungal sinusitis, frozen section was used in 8. Routine H&E stains demonstrated fungal hyphae in necrotic debris in 5 cases, often associated with vascular and perineural invasion. All patients underwent extensive sinus debridement, including orbital exenteration in 2 cases. All 12 patients died, 9 of fungal sepsis. Autopsy in 3 patients showed pulmonary involvement (2 cases), intracranial spread (1 case), and no residual fungus (1 case). Inexperience with organism recognition is surmountable. Frozen section has a role in the management of this devastating disease.