Background: Lichen planus (LP) is a common, pruritic, inflammatory mucocutaneous disease. There are several opinions and approaches to the etiopathogenesis of LP. Immunologic mechanisms almost certainly mediate its development. T-cell-mediated immunity plays the major role in triggering the clinical expression of the disease. The cytokines that are produced by lymphocytes also play an important role in the development of LP. Objective: The goal of our study was to investigate the possible role of tumor necrosis factor α (TNF-α) in the pathogenesis of LP. Methods: Serum TNF-α levels were determined with the enzyme-linked immunosorbent sandwich assay method in the sera of 40 patients suffering from LP and in those of 40 healthy controls. Results: The serum levels of TNF-α were found to be significantly higher in the patient group compared to the healthy controls (patients: 35.64 ± 9.59 pg/ml, controls: 15.6 ± 3.97 pg/ml, p < 0.001). Conclusion: Our results revealed that TNF-α might play a major role in the pathogenesis of LP.