Objective: Oral cancer is an increasingly growing health care burden in many parts of the world. Due to the relatively low prevalence of oral cancer, screening will lead to a low yield and a high proportion of false positive results. Clinical examination without histologic diagnosis can lead to misdiagnosis in over 40% of cases, especially when premalignant lesions are involved. However, clinical examination is effective especially in detecting the early stages of oral cancer, particularly in high-risk patients, such as smokers and alcoholics. The purpose of the current paper is to describe several cases of failure to diagnose lesions in the oral cavity during clinical and radiographic examinations, and to discuss how these diagnosis failures may be mitigated. Method and Materials: A series of three cases of oral tumors ranging from benign to malignant that were not recognized and referred in a timely manner, are presented. Conclusion: The difficulties faced by clinicians in diagnosing oral lesions are elucidated in this case series. The current case series, presenting instances in which pathologies were not detected and/or treated in spite of obvious signs, should serve as a warning for dental professionals. The general practitioner is the "first line of defense" for symptomatic and asymptomatic patients, and therefore the implementation of well-established screening protocols is of paramount importance. In light of the low sensitivity ratio of oral examinations, use of biopsies is mandatory when a lesion is suspected. Keywords: biopsy, clinical examination, diagnosis, oral tumors