The practice of irradiating enlarged thymus glands in infants and children began a little over a half century ago (1) and at the time was considered a great stride forward in the effort to reduce the hazard of status thymicolymphaticus. Prior to this, surgery was the principal method of treatment, offering the alternatives of exopexy or the excision of the enlarged thymus gland. One can still remember vividly the dilemma which confronted those who treated children before antibiotics became a part of our therapeutic armamentarium; the sudden death of an infant from suffocation was witnessed all too often. According to Marine (2), who gives an excellent review of the whole subject of status thymicolymphaticus and mors thymica, the priority for having described this entity goes to Felix Plater. Plater in 1614 reported the sudden death of a boy of five months, with thymic enlargement found at necropsy, and referred to 2 other boys in the same family dying suddenly with the same symptoms. For over three hundred and twenty-five years, unwarranted publicity was given the assumption that thymic enlargement accounts for much mortality in infancy and childhood. The whole controversial subject of status thymicolymphaticus was debated for years with much heat and little light, by protagonists like Symmers (3) and antagonists like Greenwood and Woods (4) and Young and Turnbull (5), who collected and analyzed many different data. It was particularly difficult to refute certain generalizations which were supported by evidence based on careful observations of outstanding clinical teachers. Chevalier Jackson, for example, in 1907 demonstrated an enlarged thymus roentgenographically, which on bronchoscopic visualization was shown to produce a scabbard deformity in the trachea (6). The use of ionizing radiation as a prophylactic measure against status thymicolymphaticus in infancy and childhood gained in popularity in many areas during the succeeding years. It should be emphasized, however, that there always existed nuclei of opposition to this practice. Kennedy and New (7) pointed out that chronic stridor in childhood need not be attributed to thymic enlargement and discouraged the use of irradiation. Eventually, the pendulum did swing away from roentgen therapy, particularly after abandonment, on scientific grounds, of the belief in sudden death from status thymicolymphaticus as a commonplace occurrence. Additional evidence came to light with autopsy demonstration of extensive microbial infections of the respiratory tract associated with episodes of sudden death (8). Over the years suspicion mounted that some latent untoward effects were associated with previous exposure to ionizing radiation; this, in turn, led to a number of studies on patients who developed such diverse sequelae as aplastic anemia (9), carcinoma of the thyroid (10), acute leukemia, and other forms of neoplasia (11, 12).