Abstract
A survey of cases of agenesis of the corpus callosum was carried out to examine its associations, utilising the British Neurological Surveillance Unit (BNSU). Fifty six cases were reported (36 male), 37 were adults. Nearly two thirds had epilepsy; half of the adult cases had intellectual impairment as estimated clinically, and a third a psychiatric disorder. Nine cases (five adults) were apparently normal neurologically, and may have escaped detection but for a coincidental or minor disorder leading to neurological investigation. The BNSU is a valuable aid in the study of rare disorders but in less severe conditions, such methods of ascertainment inevitably underestimate prevalence and are prone to selection bias towards patients with associated morbidity.