Mucormycosis is the most acutely fatal fungus infection of man. The disease causes a characteristic pattern of clinical symptoms and signs, prompt recognition of which will permit immediate institution of antifungal therapy. Personal experience with 16 cases of the rhino-orbitocerebral form of mucormycosis is the basis of this report. The first of these patients was seen in 1959, and the last in 1981. All of the patients had one or more preexisting diseases, as follows: (1) diabetes mellitus, 13; (2) acute leukemia, 3; (3) terminal carcinomatosis, 1; and (4) chronic sinusitis, 1. The most common initial symptoms and signs were sinusitis, pharyngitis, nasal discharge, and orbital/periorbital pain. Proptosis and formation of a black eschar were only seldom among the initially apparent features. Hyphas were demonstrated in tissue sections in 14 of the 16 patients in whom biopsy was done. Rhizopus species were cultured in 11 of the 13 patients from whom material for culture had been obtained clinically. Five of the 16 patients survived. All of them had been treated with surgical debridement and with intravenous amphotericin B.