ABSTRACT.The epidemiology of infantile hydrocephalus (IH) in the birth years 1983‐86 was investigated in the south‐western health care region of Sweden. The study was made as a continuation of a previous one which had shown a significant increase in the prevalence of IH in 1967‐82. That rise was entirely referable to the relatively larger number of preterm IH infants born in 1979‐82 and was considered to be due to the enhanced survival, especially of very preterm infants. The present series comprised 57 liveborn IH infants‐27 preterms and 30 born at term. The livebirth prevalence of IH was 0.64 per 1000, 0.30 for preterm and 0.34 for fullterm infants. The high prevalence of preterm IH infants in 1979‐82 had persisted, but had not increased further. This might indicate an improved outcome in preterm survivors in the period 1983‐86, as the survival rate had continued to increase. The striking predominance of a perinatal aetiology of IH in very preterm infants could be confirmed: 90 % had had intraventricular haemorrhages verified by ultrasound in the postpartum period. The outcome in very preterm surviving infants with IH was still alarmingly poor: 78% had cerebral palsy, 72 % mental deficiency, and