Background: Late diagnosis and improper treatment lead to many avoidable deaths in patients suffering from oral cancer. This study evaluated the knowledge and perceptions of general dentists regarding oral precancerous lesions and oral cancer risk factors with reference to early diagnosis and referral. Materials and Methods: In this descriptive study, 200 private general dental practitioners were randomly selected in Tehran, Iran. Demographic information and years since graduation were recorded; knowledge levels were evaluated with a standardized questionnaire consisting of 15 closed-response item questions about precancerous lesions and oral cavity cancer. Each correct answer got one point. Results: Out of 200 selected dentists, 153 returned completed questionnaires. The average age of participants was 36 and the average achieved score was 7.96 out of 15 (Min 3, Max 13). Most (64.7%) of participants were in the group that graduated within the previous 10 years, 23.5% between 10 and 20 years since graduation, and 11.8% more than 20 years previously. There was a statistically significant difference between the most recently graduated group (< 10 years) and the other two groups. The dentists' awareness was also significantly dependent on age. There was no statistically significant difference in awareness between male and female dentists. Conclusion: As professional oral health care providers, dentists should be aware of all aspects regarding precancerous lesions in order to optimize early diagnosis and referral of oral cancer patients. Training courses and continuing education seem to be an essential strategy to increase and maintain knowledge of this group.