This report describes the prevalence of non-cavitated and cavitated carious lesions in 911 randomly selected children in grades one through three on the Island of Montreal, Quebec, Canada. The criteria for diagnosis were developed for a longitudinal epidemiological study of restorative treatment decisions by dentists practising under a provincial dental insurance program for children. The intra- and inter-examiner reliability correlation coefficients of the two examiners were excellent (Kappa > or = 0.80). The most frequent carious lesion found in the examined children were non-cavitated carious lesions (incipient) within 1.5 of the gingival line on smooth tooth surfaces, and stained or non-cavitated carious lesions on pits and fissures. Out of 911 children in the study, 19.6% had sealants. Children whose parents completed a university education had a significantly lower prevalence of non-cavitated and cavitated carious lesions and fillings, and a significantly higher mean number of sealants than children whose parents had only primary school education. Education status of the parents was a significant risk marker of children with high caries experience and these children had a significantly higher mean number of non-cavitated carious lesions. This study has found that non-cavitated carious lesions are significantly more prevalent than cavitated carious lesions in children.