Objective: To assess the knowledge and preventive attitudes that Spanish dentists have towards oral cancer, before and after an educational intervention. Methods: A quasi-experimental study based on a nationwide intervention. All Spanish dentists were offered an on-site course on oral cancer. An individual questionnaire was administered before and after attending the course. The main outcome measures were systematic examination of the oral cavity, promotion of healthy habits and knowledge of clinical aspects. Results: 440 GDPs entered the study. Age: 40.7±10.7, range 21-74. Professional experience: 13.9±8.9 years, range 0-45. Of those who participated in the study, 53.1% had never attended a course on oral cancer, 72.4% stated that they perform a systematic examination of the oral mucosa, 88.2% provided systematic counselling on tobacco cessation, and 54.7% reported that they did the same for alcohol. In addition, 32.3% advised patients to eat fruits and vegetables high in antioxidants. Professional experience was significantly associated with oral mucosa systematic examination (t= 2.9; p=0.003), advice on alcohol consumption (t=5.0; p=0.000), and on fruit and vegetable intake (t=5.1; p<0.001). None of these practices were specifically associated with knowledge on oral cancer. All areas of knowledge examined showed statistically significant improvement after the educational intervention. Conclusions: The intervention appears to have improved the GDP´s knowledge, confirming the importance of this national campaign.