The aim of this population-based study is to investigate IQ and IQ-related factors in children with hydrocephalus (HC). Psychometric intelligence was assessed in subjects below the age of 7.3 years (N=52, F=18, M=34) with the Wechsler Preschool and Primary Scale of Intelligence - Revised (WPPSI-R) and for children above the age of 7.3 years (N=29, F=6, M=23) with the Wechsler Intelligence Scale for Children - Revised (WISC-R). The controls were matched according to age, gender, and geographic variables. All children were living in western Norway. 57 children had infantile HC (IH) and 24 had childhood HC (CH). Children with myelomeningocele (MMC), traumatic brain injury (TBI), or intracranial tumours were excluded. IQ levels were found to be significantly higher in the control group than in the HC groups. The Kaufman factors showed a similar pattern, with lowest values in IH, and CH intermediate between IH and NC. The results demonstrate that HC affects IQ. More specific cognitive profiles, such as non-verbal learning disabilities, are not detectable when using the Wechsler tests. For this purpose, other tests and models for analyses may be recommended.