Good syndrome is a rare, adult-onset primary immunodeficiency suspected in patients who exhibit hypogammaglobulinemia and low levels of B cells along with a benign thymic tumor (thymoma) on chest X-ray. Symptoms include frequent opportunistic infections involving the sinuses and lungs, including severe CMV disease, P. carinii pneumonia, and mucocutaneous candidiasis. The cause of Good syndrome remains unknown.

• Good syndrome occurs in 3-6% of individuals with thymomas.
• In the United States, the incidence of thymoma is approximately 0.15 cases per 100,000, and this tumor can be found in up to 10% of individuals with adult-onset hypogammaglobulinemia. On the other hand, the incidence of hypogammaglobulinemia is between 6–11% in individuals with thymoma.
• It has been estimated that Good syndrome is the underlying cause of immunodeficiency in 1% to 2% of individuals with primary antibody deficiency who are on immunoglobulin replacement treatments.