Blastomyces dermatitidis is a dimorphic fungus that causes the systemic pyogranulomatous disease known as blastomycosis. Blastomycosis most often involves the lungs, skin, and may involve nearly every organ in the body. It is difficult, however, to diagnose blastomycosis in the early stage of pulmonary disease because clinical manifestations are varied from subclinical infection to acute respiratory distress syndrome. Since blastomycosis is often accompanied by granulomatous inflammation in histopathologic findings, differentiation from other etiologic diseases is important. We report a case of a 45-year-old male with pulmonary blastomycosis who had been misdiagnosed with tuberculosis for 3 months.