With the increased number of immunocompromised patients there has been a concomitant increase in patient morbidity and mortality due to fungi. The etiologic microorganisms vary depending upon the type of immune dysfunction. Patients with malignancies and chemotherapy-induced neutropenia commonly are infected with Candida and Aspergillus. Other ubiquitous fungi such as Rhizopus, Fusarium, and Trichosporon are more frequently implicated as agents of disease in these patients. Patients with cell-mediated immune dysfunction such as acquired immune deficiency syndrome (AIDS) are susceptible to mucocutaneous candidiasis and pulmonary and disseminated cryptococcosis. Histoplasmosis and coccidioidomycosis have been particularly lethal infections in AIDS patients. Contributing factors such as broad-spectrum antibiotic use, intravenous catheterization, malnutrition, hyperalimentation, multiple surgical procedures and/or trauma, and steroids used either singly or in combination may also predispose patients to invasive fungal disease. Definitive diagnosis is often difficult to establish and usually requires invasive biopsy. Delay of culture results due to the time required to process specimens and to allow the fungus to grow also contributes to the poor results of therapy. Biopsy of skin lesions represents a useful technique for making a diagnosis. Recent advances in antifungal therapeutics promise to change the current approach to treatment for several of the mycoses. The availability of new oral azoles with spectra of activity that include aspergillosis and cryptococcosis, which currently require treatment with parenteral amphotericin B, may prove practical for prolonged oral therapy of otherwise lethal mycoses.