The study objective was clinical assessment of the efficacy of photodynamic therapy (PDT) in the treatment of oral lichen planus (OLP). There were 23 patients aged 31-82 included in the study with oral lichen planus diagnosed clinically and histopathologically. In all patients photodynamic therapy was performed with the use of chlorin e6 (Photolon(®)), containing 20 % chlorin e6 and 10 % dimethyl sulfoxide as a photosensitizer. PDT was performed using a semiconductor laser, with power up to 300 mW and a wavelength of 660 nm. A series of illumination sessions was conducted with the use of superficial light energy density of 90 J/cm(2). Changes of lesion size were monitored at one, two, five, and ten PDT appointments from the series of ten according to the authors' own method. The sizes of clinical OLP lesions exposed to PDT were reduced significantly (on average by 55 %). The best effects were observed for the lesions on the lining mucosa (57.6 %). The therapy was statistically significantly less effective when masticatory mucosa was affected (reduction, 30.0 %). Due to substantial efficacy and noninvasiveness, PDT can be useful in the treatment of OLP lesions.