Oral exfoliative cytology can be a powerful tool for early detection of malignant and premalignant lesions as well as for some viral and fungal infections, if the limitations of the method are thoroughly understood and appreciated by the dental clinician. The rationale for oral cytology is developed and documented, and interpretations of the results are explained. Advantages and disadvantages of this technique are given and indications and contraindications for this diagnostic adjunct are discussed. A simple method involving the use of inexpensive equipment in the office is suggested.