A 51-year-old male patient with diabetes mellitus complicated by ketoacidotic imbalance developed a rhinocerebral mucor mycosis that advanced despite early amphotericin B therapy and extensive surgical intervention. The MIC of amphotericin B for the isolated mucor species was 64 mg/l, meaning that in vitro resistance also existed. Only long-term treatment with ketoconazole (600 mg/day, perorally) was successful in curing the disease.