The role of dentists in both primary (promoting a healthier lifestyle) and secondary (early diagnosis) prevention of oral cancer is undeniable, and becomes particularly important as oral cancer is thought to be preceded by premalignant lesions or conditions in about one half of the cases. In these situations, there is the possibility for an early diagnosis which will definitively influence the survival rate. Thus, it is an undergraduate educational objective related to secondary prevention of oral cancer to increase the efficacy of screening of precancerous lesions/conditions. A questionnaire with 38 clinical cases including 16 benign lesions, 9 malignant lesions and 13 precancerous lesions or conditions was applied voluntarily to 3rd, 4th and 5th year University of Santiago de Compostela dental students on April 1996. The participation rate was 90% of the 3rd-year students, 60% in 4th-year class, and 50% of the 5th-year group. The agreement in the diagnosis with a panel of experts reached 81.45% for 5th-year students. Students of 3rd- and 4th-year scored lower percentages, probably due to the rarity of some of the conditions in our area. 5th-year students scored significantly higher values than 3rd-and 4th-year students.