Although there is very little epidemiological evidence on the prevalence and severity of erosion in children and adults, there have been recent case reports suggesting that the problem of erosion is increasing. This study describes the use of a simple reproducible erosion index. A total of 178 four-year-old children were assessed; almost half of these children showed signs of erosion. The most common site affected was the palatal surface of the upper incisors with 17 percent of the children examined showing visible dentine for greater than one third of the tooth surface. When considering the influence of socioeconomic group on the prevalence of erosion, four out of five children examined in the low socioeconomic group showed low levels of erosion, while a much greater prevalence was observed in the higher socioeconomic groups.