During the past decade, as part of an ongoing longitudinal study (the Ottawa Prenatal Prospective Study - OPPS) we have reported an association between in utero exposure to cigarettes and deficits in auditory based behaviour. The present report is based upon the findings of 131 children betwen the ages of 9-13. We describe a dose-response relationship between particular aspects of reading skills and in utero cigarette exposure. The processes involved that appear vulnerable to maternal prenatal smoking are those with auditory underpinnings. They include phonological analysis - the association of sounds with letters or combination of letters - and the knowledge of grammatical structure based on auditory processing. The results also suggest that the impairments identified in reading ability differ somewhat from those observed in children diagnosed as dyslexic.