This study examined 35 patients with developmental disabilities who were referred for diagnostic evaluation that later revealed agenesis of the corpus callosum (ACC) by computerized tomography (CT). Sixteen had partial ACC, six had complete ACC, and one had a hypoplastic corpus callosum. In the other twelve cases, ACC existed, but the degree of callosal defect was not specified. Other intracranial defects were frequently present. Clinically, 15 patients (43%) had a history of seizures, 28 (82%) were mentally retarded or developmentally delayed and an additional five patients (15%) possessed borderline intelligence, and 10 (29%) had cerebral palsy. Ocular, spinal, and orofacial abnormalities were often present. Detailed summaries of these findings are given in Table I. Although several genetic causes of ACC have been identified, in the vast majority, the etiology is assumed to be multifactorial. In our study, two patients had trisomy 8 mosaicism and 11 (35%) had a family history of developmental disability. A review of the literature on chromosomal abnormalities in acalossal patients revealed 81 additional cases, which are discussed and outlined in Table II.