PURPOSE: The aim of this prospective study was to investigate the diagnostic accuracy of DNA image cytometry in combination with non-invasive brush biopsies taken from suspicious oral lesions. MATERIAL AND METHODS: Cytological diagnoses obtained from 1328 exfoliative smears of 332 different lesions were compared with histology and/or clinical follow-ups of the respective patients. Additionally, nuclear DNA contents were measured after Feulgen restaining using a TV image analysis system. DNA aneuploidy was assumed if abnormal DNA stemlines or cells with DNA content greater than 9c were observed. RESULTS; The sensitivity of our cytological diagnosis in addition to DNA image cytometry on oral smears for the detection of cancer cells was 97.8%, specificity 100%, positive predictive value 100%, and negative predictive value 98.1%. CONCLUSION: The application of DNA image cytometry with DNA aneuploidy as a marker for neoplastic transformation in oral smears secures cytologic diagnosis of carcinomas. Smears from brushings of all visible oral lesions are an easily practicable, cheap, noninvasive, painless, and safe screening method for detection of oral precancerous lesions and squamous cell carcinoma in all stages. We conclude that DNA image cytometry is a very sensitive and highly specific, objective, and reproducible adjuvant tool for identification of neoplastic cells in oral smears.