No detailed information is available about the timing and correlation of objectively gauged ventricular width (VW) and the rate of growth of the occipitofrontal circumference in premature infants with intraventricular haemorrhage preceding progressive ventricular dilation. For this study, two groups were selected according to clinical course: group A (n = 6) had ventriculomegaly with no signs of raised intracranial pressure, while patients in group B (n = 7) developed progressive ventricular dilation after a period of latency. A VW between 0.9 and 1.4 cm (group A) did not affect normal head growth, whereas a VW greater than 1.5 cm was always associated with the development of hydrocephalus. Our data further suggest that the widely used criterion of a head growth rate of more than 2 cm/week is a relatively poor criterion for the definition of post-haemorrhagic hydrocephalus.