During the period January 1988 to December 1990, the overall incidence of infantile hydrocephalus in the south-western region of Saudi Arabia was 0.81/1000. The series comprised 61 infants affected by infantile hydrocephalus. The total number of live births in this period was 74,923. Hydrocephalus associated with spinal dysraphism (spina bifida cystica and encephalocoele) constituted 24 cases (39.3%), and there was aqueduct stenosis in 10 cases (16.4%). Nine cases (11.9%) were post-meningitic, and seven (14.8%) post-haemorrhagic. There was Dandy-Walker malformation in five cases (8.2%), three (4.9%) had congenital idiopathic hydrocephalus, two (3.3%) congenital toxoplasmosis, and one (1.6%) isolated Arnold Chiari malformation. There were congenital causes in 45 cases, 73.7% of all the cases in this series (incidence: 0.6/1000 births). Of the remaining 16 cases (26.3%) which were due to postnatal factors, seven (11.5%) were caused by acquired cerebral haemorrhage, only two of them being premature, and the other nine (14.8%) were due to meningitis. The data indicate the predominance of prenatal causes of infantile hydrocephalus and the relatively low contribution of extreme prematurity. This is possibly due to the high mortality of this group of infants in this region.