Oral lichen planus (OLP) carries a very small probability of becoming malignant. Our Finnish series comprised eight patients suffering from OLP and concurrent or subsequent oral squamous cell carcinoma over a 10-year period. The mean interval between the histologically suggested initial diagnosis of OLP and carcinoma was 3.4 years. An oral ulcer as a clinical manifestation of malignant change appeared in seven of these eight patients; five of the eight died of carcinoma on average 13 months (range 7-20) after the final squamous cell carcinoma diagnosis. These eight patients were compared to eight control OLP patients without malignant transformation matched as to follow-up time, age, gender, sites of the lesions, etc. We could discover no histological features leading to malignant development. However, the clinically unilateral atrophic/erosive type of OLP more often preceded the malignant change, compared to the situation for control patients, in whom the most prevalent type was the bilateral reticular OLP. However, the probability seems to be very small.