Six preterm infants who developed disproportionate enlargement of the 4th ventricle during the neonatal period, associated with post-haemorrhagic ventricular dilatation (PHVD), before shunt placement are reported. Five of the six preterm infants developed cyanotic spells and/or bradycardias at the time of rapid enlargement of the 4th ventricle, suggestive of raised posterior fossa pressure, which resolved following insertion of and drainage from a subcutaneous reservoir. In one of the three survivors an isolated 4th ventricle was subsequently diagnosed later in infancy, requiring drainage. These data suggest that a combination of an enlarged 4th ventricle on ultrasound and cyanotic spells and/or bradycardias should lead to rapid release of raised pressure in the posterior fossa. Long-term follow-up of these children is necessary, as isolation of the 4th ventricle can subsequently develop. Hydrocephalus, intraventricular haemorrhage, isolated 4th ventricle, preterm infant