The purpose of this study was to evaluate the validity and outcome of an oral mucosal screening programme conducted in Japan. All adults over the age of 40 years resident in Tokoname city were invited by letter to attend a free general health screen and oral examinations annually. Twenty- to 39-year-old females were also encouraged to participate. During the years 1996-98, a total of 19056 subjects (5885 male, 13171 female: mean age 60.7+/-11.3 years) were examined by three types of screeners: postgraduate dental residents (n=17), hospital dentists (n=5) and general dental practitioners (n=15). In the cohorts examined screening dentists recorded oral mucosal lesions in 783 (4.1%) subjects. Of those detected with mucosal lesions, 200 (25.5%) were referred and 137 (68. 5%) attended for follow up examination in hospital departments by specialists with full diagnostic back up facilities. Thirty-nine subjects were confirmed as having oral cancer or precancer (two squamous cell carcinomas, 37 leukoplakias) and 40 with lichen planus. Five false positives (3.6%) were found. Among the cases referred under other diagnostic labels no cancers were detected. Among those who attended for confirmation of oral cancer or precancer by a specialist, sensitivity, specificity and positive predictive value were 0.92, 0.64 and 0.78, respectively. In males with oral cancer/leukoplakia, the prevalence of smoking, drinking and combined habits was higher than those with lichen planus or among negative subjects. The sensitivity and specificity determined from this research suggests that the performance of the Japanese dentists employed in screening was satisfactory. An attendance of 68% for re-examination by specialists compares well with other reported studies measuring patient compliance.