ABSTRACT: A 41-year-old man was referred to the wound clinic for an enlarging 9.5 x 14-cm ulceration of the right upper arm of 8 months’ duration. A biopsy was obtained, and fungal stains showed broad-based budding spores typical of blastomycosis. He was treated with oral itraconazole, and the ulcer healed in 2 months. Blastomycosis is a systemic fungal infection acquired by inhalation of the spores of the fungus Blastomyces dermatitidis. Initially a pulmonary infection, the skin is the most common secondary site of involvement. More typically presenting as hyperkeratotic nodules, it may occur as ulcerations. Blastomycosis has significant morbidity and mortality, and in unsuspected or asymptomatic cases, the skin lesions may be the key to successful diagnosis and treatment.