The objective of this study was to examine the histological features of apparently normal oral mucous membrane adjacent to lesions of oral lichen planus. Twenty-six patients attending an oral medicine unit with clinical lesions typical of oral lichen planus had biopsies of lesional and perilesional sites. Biopsies were examined for histopathological features of oral lichen planus. Twenty-two (85%) of lesional biopsies and 12 (46%) of the perilesional biopsies were reported as either typical or showing some features of lichen planus. Twelve of these 22 cases (55%) had both lesional and perilesional biopsies reported as either typical or showing some features of lichen planus. These 12 cases represented 46% of all cases. In four cases (15%) neither the lesional nor the adjacent perilesional biopsy was reported as lichen planus. The inflammatory process in oral lichen planus may extend beyond the confines of the clinical lesion into adjacent mucous membrane of normal appearance.