Primary invasive mold infection of the oral cavity is a rare but serious complication in immunocompromised hosts. We report a case of fatal Trichoderma longibrachiatum stomatitis in a 66-year-old female patient with malignant lymphoma. The infection rapidly disseminated from the oral mucosa to the lungs during neutropenia. Despite intensive antifungal therapy with amphotericin B and itraconazole, there was a fatal progression of the condition. While Trichoderma species have been recognized to be pathogenic in profoundly immunosuppressed hosts, this is the first report of the primary oral focus causing a fatal infection.