Early detection of oral premalignant lesions (OPMLs) by visual inspection with toluidine blue has not been addressed. We conducted a community-based randomized controlled trial to assess whether using toluidine blue as an adjunctive tool for visual screening had a higher detection rate of OPMLs and could further reduce the incidence of oral cancer. In 2000, in Keelung, we randomly assigned a total of 7975 individuals, aged 15 years or older and with high-risk oral habits, to either the toluidine-blue-screened (TBS) group or the visual screening group. Results showed 5% more oral premalignant lesions and 79% more oral submucous fibrosis detected in the TBS group than in the control group. After a five-year follow-up ascertaining oral cancer development through linkage to the National Cancer Registry, the incidence rate in the TBS group (28.0 x 10(-5)) was non-significantly 21% lower than that in the control group (35.4 x 10(-5)).