The aim of this study was to determine the effectiveness of a school dental screening in encouraging school children aged 4 to 6 years to visit a dentist. One thousand five hundred and sixty-two children attending the 13 primary schools in Wallasey. Merseyside, were examined by a single trained examiner; those with urgent treatment needs or evidence of recent treatment were excluded. The remaining 528 children with signs of dental caries were entered into the study. Children within each school were stratified by age, sex and number of carious teeth and then allocated at random to test and control groups. Parents of children in the test group were advised by letter that their child would benefit from a more detailed clinical examination. A reply slip was attached to the letter and non-responders were carefully followed up. The control group received no such interventions. After 4 months, data on dental visits by both test and control group children were extracted from clinical records. Attendance data were obtained for 262 children (97 per cent) in the test group and 243 children (94 per cent) in the control group. Seventy-three per cent of the test group and 42 per cent of the control group visited the dentist over the review period; the difference of 31 per cent favour of the test group was statistically significant. Attendances at both general dental practitioners and community dental clinics were increased. The effect of the screening procedure was seen particularly in areas of lower socio-economic status.(ABSTRACT TRUNCATED AT 250 WORDS)