A 2.5-year-old girl with Crouzon's disease, hydrocephalus, and a lumboperitoneal shunt died as a result of chronic tonsillar herniation (acquired Chiari 'malformation'). The possible synergistic role of the cranial dysmorphism and the lumboperitoneal shunt in the development of this anomaly is discussed. The literature is reviewed and it is argued that if hydrocephalus occurs in infants in whom cephalocranial disproportion is likely to develop, then it is inadvisable to insert a lumboperitoneal shunt.