The Isle of Lewis is an island community which has little movement of its school population and, since the Second World War, mirrors closely the rest of the United Kingdom in availability of foods, introduction of television and educational opportunities. One of the first major dental epidemiological studies was conducted on the island by King in 1937. Between 1968 and 1984 a further series of investigations has been conducted on this population by the present authors; these allow a comparison of caries prevalence at intervals of time over 47 years. The findings show a marked increase in dental caries from 1937 to 1971, an equally marked decrease during the remainder of the 1970s and a further modest increase among the younger age groups studied between 1981 and 1984.