Oral cytopathology is a simple, non-invasive technique that could be used for early detection of oral premalignant and malignant lesions, but the effectiveness of this diagnostic approach remains controversial. The aim of this study was to evaluate the sensitivity, specificity, positive and negative predictive values, and accuracy of cytopathology for diagnosing oral squamous cell carcinoma (OSCC) and the diagnostic concordance between cytopathological and histopathological diagnoses. The study enrolled 172 patients at outpatient clinics who presented with oral lesions suspicious of malignancy. All patients underwent oral cytological scrapes followed by an incisional biopsy. Of 148 cases that were histopathologically diagnosed with OSCC, the cytopathological method diagnosed 123 positive cases and resulted in a suspicion of OSCC in 16 patients. Based on these data, the sensitivity was 83.1%, the specificity was 100.0%, the positive predictive value was 100.0%, the negative predictive value was 49.0%, and the accuracy was 85.5%. The diagnostic concordance between histopathological and cytopathological examinations was 83.1% for OSCC and 85.7% for non-neoplastic lesions. The results indicate that cytopathological diagnosis had good concordance with histopathological diagnosis and showed high sensitivity, specificity, positive predictive value, and accuracy. We conclude that the sensitivity of oral cytopathology is sufficient to justify its use as a diagnostic screening test and to confirm the malignant nature of epithelial cells, mainly for the classification of OSCC. Therefore, cytopathology may be a reliable method for referring patients who require diagnosis of suspected oral cancer for starting treatment.