Object: In the present study, we compared ventricular pressures (VP) and the progression of ventricular enlargement in a new experimental neonatal hydrocephalus model, to gain an understanding of how communicating hydrocephalus progresses. Methods: Kaolin was injected into the subarachnoid space at the cranial convexity of neonatal rats. Gross examination was performed on the 3rd, 5th and 7th days, and ultrasonographic examination on the 15th day, and at the end of the 1st and 2nd months following the kaolin application. Ventricular size indexes (VSI) were calculated in the case of a large ventricular dilatation. VPs were assessed on the 15th day, and at the end of the 1st and 2nd months, with a computerized data acquisition system. Conclusions: In the 1st and 2nd months VSIs were significantly higher than in control rats on the 15th day after kaolin administration. VP on the 15th day was significantly increased compared with that in control rats. VP in the 1st month was still high, but had subsided. In the 2nd month VP was not increased over control. In the late stages, the progression of infantile communicating hydrocephalus is not related to VP levels.