Detection of oral cancer is only depend on biopsy. We analyzed the usefulness of smear cytology in the detection of the squamous epithelial lesions of the oral cavity. The author collected a total of 54 cases of oral cytology and some corresponding biopsies from the patients who had a leukoplakia or ulceration of the oral mucosa over 12 months. Cytology slides were prepared using ThinPrep method and stained with Papanicolaou stain. The cytologic diagnoses were categorized based on The Bethesda System and the histologic diagnoses were classified as negative, oral intraepithelial neoplasia (OIN) I, OIN II, OIN III, or squamous cell carcinoma. Cytohistologic correlations were reviewed. Three cases of invasive squamous cell carcinoma, 5 cases of OIN III, and 46 cases of non-neoplastic benign lesions (including 7 cases of reactive atypia and 39 cases of within normal limit) were detected. Three cases of reactive atypia and 1 case of OIN III were confirmed as OIN I through follow-up biopsy. The cause of error was interpretation error in all cases. The concordance rate of oral cytology and biopsy was 92.6%. Oral cytology is a useful primary screen of OIN and oral cancer.