Abstract Zygomycosis, an invasive fungal infection, is usually seen in persons with diabetes, particularly in those with diabetic ketoacidosis. The infection most frequently occurs in the rhino-cerebral region and rapidly spreads, causing a swift demise. Rarely, the infection is confined to the cutaneous tissues. We describe a 31-year-old man seropositive for human T lymphotropic virus type I who had diabetic ketoacidosis with zygomycosis confined to the right arm. The lesion was presumed initially to be a bacterial infection but did not respond to conventional antimicrobial therapy. The arm lesion was cultured, and Rhizopus arrhizus was isolated. The patient responded well to a combination of amphotericin B and extensive surgical debridements. Our case emphasizes the importance of maintaining a high index of suspicion of cutaneous zygomycotic infections in the impaired host, especially of those in patients with diabetes, who do not respond to initial antimicrobial treatment.