Thymic tumors represent a unique neoplastic disease associated with various immune-mediated syndromes. Immune impairment is generically recognized to be associated with thymoma. Hypogammaglobulinemia and recurrent pulmonary infections in thymoma patients define Good's syndrome. Apart from sporadic reports focusing on this topic, there is still a lack of knowledge on immune assessment and clinical sequelae in thymoma patients. The present study was performed to evaluate immunoglobulin levels, CD19(+) B lymphocytes, and CD3(+) T lymphocytes in a large series of thymoma patients from a single institution. The occurrence of recurrent severe infections was related to immunological findings to identify the possible correlation with the immunodeficiency status. Eighteen patients (eight males, ten females, mean age: 56 years, range: 19-75) with a pathological diagnosis of thymic tumor were studied. Six patients suffered from clinical recurrent pulmonary infections. Blood samples were collected to measure serum immunoglobulins and analyze immunophenotype. Low T lymphocyte number was found in 22% of the patients. T lymphocytosis was present in one patient. Panhypogammaglobulinemia was found in 4 of 18 patients (22%). Conversely B lymphopenia was a frequent finding in this series of thymoma patients (9 of 18, 50%). Five of six patients (83%) with recurrent infections had B lymphopenia, while only two (33%) had panhypogammaglobulinemia. B lymphopenia often occurred in this series of thymoma patients and was related to susceptibility to recurrent infections more than hypogammaglobulinemia. Therefore, immunophenotype has to be monitored in follow-up of thymoma patients because it may reveal significant abnormalities.