"Non-Aromatic Very rich in Steranes" (NAVS) naphthalan is a purified natural oil derivative, abundant in steranes (geogenic "steroids"). The purpose of this study was to evaluate the effectiveness of NAVS in the treatment of oral lichen planus (OLP) and recurrent aphthous stomatitis (RAS). We used NAVS oil in adhesive paste in 11 patients with clinically and histologically proven OLP (open label), and in 7 patients with RAS (double blind randomized; topical betamethasone in adhesive paste used as control). The severity of the OLP lesions was objectively scored. The number and diameter of RAS lesions were assessed on days 0, 3, and 5. The intensity of pain and discomfort was determined using visual analogue scale (VAS) and "Oral health impact profile" (OHIP-14) before and after therapy. OLP cumulative activity scores on days 0 and 28 were 101.5 and 48.5, respectively (t=5.99; P=0.0001). Using NAVS for 28 days resulted in 52.2% overall clinical improvement. Cumulative OHIP-14 scores on days 0 and 28 were 210 and 142, respectively (t=5.65; P=0.0002). Out of a total of 7 patients with RAS, 4 of them were treated with NAVS and 3 with topical corticosteroids. There were no statistically significant differences in improvement rate between the two groups (lesion number (day 3 P=0.29; day 5 P=0.32); lesion diameter (day 3 P=0.64; day 5 P=0.74)). NAVS successfully reduced the clinical signs and symptoms of OLP, and reduced the number, diameter, and symptoms in patients with RAS, statistically comparable with corticosteroids.