Microcephaly results from inadequate brain growth during development. It may develop in utero, and therefore be present at birth, or may develop later as a result of perinatal events or postnatal conditions. The aetiology of microcephaly may be congenital (secondary to cerebral malformations or metabolic abnormalities) or acquired, most frequently following an ischaemic insult. This distinct radiological and pathological entity is reviewed with a specific focus on aetiology.