Using standard epidemiological techniques, several indicators of dental health showed significantly lower levels of caries experience in 5-year-old children from fluoridated Anglesey compared with a similar group from non-fluoridated mainland Gwynedd. The mean dmft was 0.80 in Anglesey and 2.26 in mainland Gwynedd. The mainland Gwynedd children had suffered more toothache and experienced more dental extractions. This study showed that fluoridation of water supplies remains an effective and relevant public health measure, and illustrates the value of a parental questionnaire in epidemiological surveys of younger children.