Thirteen cases of the Dandy-Walker syndrome were seen over a period of 12 years. In this study their preoperative evaluation, surgical treatment and outcome is reviewed. The incidence of hydrocephalus in the series was 77%. Eight of the patients had associated central nervous system anomalies, and the need to identify these abnormalities is stressed. Because the two conditions require different surgical management, during the diagnostic work-up it is crucial to differentiate between the Dandy-Walker syndrome and extra axial cerebrospinal fluid (CSF) filled cysts, and to establish the patency of the aqueduct. The reliability of different diagnostic methods is discussed and the value of metrizamide computed tomographic ventriculography is emphasized. Unsatisfactory results following membrane excision in early cases, and observations of CSF dynamic disturbances confirm the futility of the direct approach for the management of the Dandy-Walker syndrome. The aqueduct was invariably patent and allowed either primary cyst or ventricular shunting, although simultaneous double shunting using a 'Y' connector may need to be carried out later. The mortality rate for the series was 18%. At follow-up 54.5% of the children were judged to have normal IQs.