Adenylosuccinase deficiency, an autosomal recessive inborn error of purine synthesis, was first described in 1984 by Jaeken and Van den Berghe (reviewed in J Inher Metab Dis 20;1997:193). The cardinal features are variable psychomotor delay often accompanied by epilepsy and autistic features. Diagnosis is made by detection of abnormal purine metabolites in body fluids. We report a girl who presented with early onset epilepsy, associated with acquired microcephaly and severe psychomotor retardation, as the most prominent symptoms.