Larynges from 17 patients with DiGeorge syndrome (DGS) and from 14 patients with tetralogy of Fallot (TOF) (11 non-DGS and 3 possible but unproven DGS) were dissected, measured, and compared to a control population of comparable body length. The patients with DGS and the 3 patients with TOF suspected of having DGS showed the following: small thyroid cartilages with increased anterior angle, abnormally short superior cornua, low ratio of mean superior cornual length to distance between superior cornual tips, and delayed time of maximal rate of increase in superior cornual length relative to increase in body length. The hypoplasia, delayed maximal growth rate and persistent fetal shape of the thyroid cartilage (predominantly a derivative of the fourth branchial arch) in DGS, indicates that the causative process in the syndrome affects not only the third and fourth branchial pouches, but also, by a contiguous field defect, other derivatives than great vessels of the fourth-sixth branchial arches.