THE FUNCTIONS of the thymus gland have bewildered investigators since Galen, in the second century AD, called the thymus the "organ of mystery." Some of this mystery was unveiled in 1939 when Dr. Alfred Blalock, who was then at the Vanderbilt University Hospital, reported the successful excision of a thymic tumor in a 19-year-old white woman with myasthenia gravis.1 Relatively little knowledge regarding thymic tumors has accumulated since this time, although other clinical syndromes occurring with thymic tumors have been reported. In addition to the coexistence of thymoma and myasthenia gravis reported by Weigert2 in 1901, agenesis of erythrocytes,3,4 agammaglobulinemia,5 and Cushing's syndrome6 are now recognized. In an attempt to obtain more information regarding thymic tumors, we have reviewed the surgical experience with thymoma at the Vanderbilt University Medical Center for the past 15 years. Despite the pioneering efforts of Blalock, thymomas have been infrequently