The DiGeorge anomaly (DGA), originally considered a clinical paradigm for isolated thymus deficiency, has now been redefined as a member of a group of disorders that share in common a chromosome deletion, which results in monosomy 22q11 (CATCH-22 or DiGeorge/velocardiofacial [VCFS] syndrome). In addition to the thymus defect, conotruncal heart anomalies, dysmorphism, hypoparathyroidism, and cleft palate are prominent features. Despite the emphasis on thymus involvement in DGA, a clinically significant thymus defect is found only in a small percentage of these patients. The basic embryological fault in these disorders is an inadequate development of the facial neural crest tissues, resulting in defective organogenesis of pharyngeal pouch derivatives. Although first described by an endocrinologist, this experiment of nature has become a major subject of investigation for geneticists and immunologists. Elucidation of the etiology and attempts to effectively treat the diverse clinical problems continue to challenge and stimulate many disciplines of medicine both in the laboratory and at the bedside.