Object The optimal management of neonatal intraventricular hemorrhage (IVH) and posthemorrhagic ventricular dilation is challenging. The importance of early treatment has been demonstrated in a recent randomized study, involving early ventricular irrigation and drainage, which showed significant cognitive improvement at 2 years. The objective of this study was to define the changes in CSF absorption capacity over time in a neonatal piglet model of IVH. Methods Ten piglets (postnatal age 9–22 hours) underwent intraventricular injection of homologous blood. A ventricular access device was inserted 7–10 days later. Ventricular dilation was measured by ultrasonography. Serial constant flow infusion studies were performed through the access device from Week 2 to Week 8. Results Seven piglets survived long term, 43–60 days, and developed ventricular dilation; this reached a maximum by Week 6. There was no significant difference in baseline intracranial pressure throughout this period. The resistance to CSF outflow, R_out, increased from 63.5 mm Hg/ml/min in Week 2 to 118 mm Hg/ml/min in Week 4. Although R_out decreased after Week 5, the ventriculomegaly persisted. Conclusions In this neonatal piglet model, reduction in CSF absorptive capacity occurs early after IVH and accompanies progressive and irreversible ventriculomegaly. This suggests that early treatment of premature neonates with IVH is desirable.