The clinical, pathologic and immunologic features of 27 patients with chronic mucocutaneous candidiasis and thymic tumors are reviewed. This form of chronic candidiasis is unique in that the infections do not occur until after the third decade and, in contrast to patients in whom candidiasis develops during infancy or childhood, it is not accompanied by failure of endocrine organs. Instead, the patients have the disorders that often accompany thymoma, such as myasthenia gravis, hypogammaglobulinemia, and abnormalities of the bone marrow and circulating blood elements. Evidence of impaired cell-mediated immunity was found in 16 of the 21 patients in whom studies were made. The pathogenesis of the immunodeficiency in these patients is unknown. Immunosuppressive activities in the plasma of four patients were found, but none of the five patients in whom the appropriate studies were made was found to have suppressor cells. The features of this disorder are unique enough that it should be considered a syndrome, and patients in whom candidiasis develops during their adult years should be studied for the presence of thymoma.