Lichen planus (LP) is a chronic recurrent rash of unknown cause with no established cure. Clinical and immunohistochemical studies strongly support an immunologic basis for the disease. There has been growing evidence suggesting a role for transforming growth factor β1 (TGF-β1) in the pathogenesis of LP.The aim of the present study was to investigate the possible role of TGF-β1 in the pathogenesis of LP.TGF-β1 was analyzed on skin biopsies of 25 patients presenting with LP and 10 age-matched and sex-matched normal subjects (controls).TGF-β1 was expressed in keratinocytes of 70% of the control group and 48% of LP cases with a significant difference in intensities of expression (P=0.01). In LP, moderate intensity of keratinocyte expression was significantly associated with frequent apoptosis (P=0.04). Dermal lymphocytes showed positive expression in 80% and intense expression was significantly associated with absent hyperkeratosis (P=0.03). Only 2 cases showed mild expression in epidermal lymphocytes.Reduced TGF-β1 expression in LP may participate in immune dysregulation of the disease.