Congenital hypoparathyroidism typically manifests with hypocalcemia with or without associated characteristic physical findings and is usually diagnosed during the neonatal period. This report describes an African-American male who was diagnosed at age 32 yr to have dysgenesis of the parathyroid glands due to chromosome 22 microdeletion. Symptomatic hypocalcemia did not develop until age 14 yr, a few weeks after initiation of anticonvulsant therapy for generalized tonic-clonic seizures. Because of the timing for onset of symptomatic hypocalcemia, it was presumed that the patient had anticonvulsant-induced hypocalcemia, and he carried that diagnosis for 18 yr. Chromosome 22q11 deletion syndrome was first suspected at age 32 yr, based on the findings of subtle dysmorphic facial features and a history of learning disability in a patient with PTH-deficient hypocalcemia. The diagnosis was confirmed by fluorescence in situ hybridization analysis. This case underscores the variable clinical presentation of this congenital form of hypoparathyroidism. Chromosome 22q11 microdeletions are relatively common, and the diagnosis should be considered even in adults with hypoparathyroidism because of the potential benefit of genetic counseling.