Oral cytology may distinguish benign, dysplastic or malignant cells. However, it is not a substitute for biopsy. Rather, it is a useful adjunct in the diagnosis of oral surface lesions due to cancer, viral disease, vesiculobullous lesions or fungal infection. This painless, atraumatic and simple technique for collecting a sample of superficial cells is used extensively in the diagnosis of less visible accessible lesions, such as those in the uterine cervix or the lung. The emphasis here is placed on the role of detecting and monitoring premalignant lesions and squamous cell carcinoma of the mouth.