Hearing impairment is a substantial worldwide problem mainly affecting the adult population. The prevalence of permanent childhood hearing impairment (PCHI) is relatively small (1 in 752) but the effects of PCHI are substantial. Children with PCHI (aged 4-12 years; n = 100) who use spoken English as their first language were assessed for cognitive and behaviour performance (controls included hearing children and children with otitis media with effusion). There was a trend in performance across severity for all assessments, with about a 2 SD difference for IQ between hearing controls and PCHI, causing concern for the pervasiveness and impact of even moderate PCHI.