The endemic fungi Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides immitis are primary human pathogens whose major portal of entry is the respiratory tract. Their clinical manifestations are categorized as acute, chronic or chronic progressive, or disseminated fungal disease. Most acute pulmonary infections are self-limited, and many are asymptomatic. Chronic, progressive, or disseminated disease is much less common and most often occurs in immunocompromised patients. The radiologic manifestations of these disorders are protean. They include interstitial or air-space opacities, solitary or multiple pulmonary nodules, parenchymal masses, cavities, and hilar or mediastinal adenopathy. The diagnosis of a thoracic mycosis requires familiarity with the epidemiology of the fungus in question, the various modes of clinical presentation, and the full spectrum of radiologic manifestations. Although skin and serologic tests can be useful, definitive diagnosis requires culture of the fungus from infected tissue or demonstration of the organism at microscopic examination.