Objective: To describe the periprocedural use of a lyophilized platelet product during rhinoscopic diagnosis and treatment of sinonasal aspergillosis in a Greater Swiss Mountain Dog with a P2Y12 platelet receptor disorder.Case Summary: After the development of severe epistaxis, a Greater Swiss Mountain Dog was diagnosed with thrombopathia secondary to a P2Y12 receptor gene mutation. Concurrent primary nasal disease was also suspected due to persistent mucopurulent nasal discharge. One month after the initial presentation for epistaxis, the dog was readmitted for workup of nasal disease. Computed tomography of the head showed turbinate lysis and regional lymphadenopathy. Because of concern for a high risk of bleeding in a thrombopathic patient subjected to rhinoscopy and nasal biopsies, a lyophilized platelet product was administered prior to the procedure. Rhinoscopic exam revealed fungal plaques consistent with Aspergillus spp. that were later confirmed on fungal culture to be Aspergillus fumigatus. Rhinoscopic biopsies were performed as well as debridement of the fungal plaques, followed by topical administration of clotrimazole solution. Bleeding was minimal during and after the procedure, and the dog recovered uneventfully.New or Unique Information Provided: This is the first report of the prophylactic use of lyophilized platelets in a thrombopathic patient undergoing an invasive procedure with potential for significant hemorrhage. Minimal bleeding occurred during the procedure, suggesting that lyophilized platelets could be used for the prevention of bleeding in thrombopathic patients undergoing invasive procedures.