Mucormycosis is a rare, sometimes severe fungal infection that has emerged as a possible complication of COVID-19. We report a case of a non-diabetic, apparently immunocompetent patient diagnosed with rhino-orbital-cerebral mucormycosis shortly after COVID-19 treatment with dexamethasone. The patient received optimized systemic antifungal therapy and extensive surgical treatment. So far, four months after the last hospital discharge, the patient has been in good general condition. This case is a dramatic reminder that beneficial corticosteroid therapy in general inevitably carries a risk of opportunistic infection, and corticosteroid therapy for COVID-19 risks orbital-rhinocerebral mucormycosis that clinicians should watch for with vigilance.