We have presented a case illustrating that an asymptomatic, red lesion in the oral mucosa should be considered a malignant neoplasm, until proved otherwise. A biopsy and microscopic examination of such lesions are necessary to establish a definitive diagnosis. An appropriate method of obtaining a tissue specimen from the floor of the mouth has been described, and the importance of taking a comprehensive clinical history has been reviewed. The value of transmitting this information to the pathologist, who examines the removed tissue, has been stressed. Small, asymptomatic erythroplastic lesions of the oral mucosa that have not resolved or responded to treatment with two weeks should have a biopsy examination.