The site and size of 222 asymptomatic, primarily erythroplastic, cancers of the oral mucosa in 161 patients have been prospectively documented. Of 207 intraoral lesions (excluding 15 of the lip), 201 (97.1%) were found in three locations; floor of the mouth (101), ventral or lateral tongue (36), and soft palate complex (64). Of the 101 in the floor of the mouth, 73 occurred in the anterior portion with 33 involving the papilla at exit of Wharton's Duct (submaxillary gland). Of the cancers 84.2% were 2 cm or less and 41.9% were 1 cm or less. Of the lesions 2 cm or less 70.6% were invasive carcinoma. Minimal size does not preclude invasiveness. In view of the apparent predilection of oral carcinoma for particular sites (where there is no obvious agent), rather than random occurrence, the three aforementioned sites are designated as high risk areas which deserve particular scrutiny in an examination of the oral cavity. It is incumbent upon the clinician to biopsy all asymptomatic, persisten (14 days or more) mucosal aberrations in the high risk areas, especially those with erythroplastic components, regardless of size.