One hundred forty-nine patients attending Edinburgh Dental Hospital had oral keratosis diagnosed clinically and histologically. The keratoses were grouped into erosive and nonerosive lichen planus, other keratoses infiltrated with inflammatory cells, and noninfiltrated keratoses. Drug histories were obtained from each patient on presentation, and the groups were analyzed to assess the association between the ingestion of commonly prescribed drugs and oral keratoses. Patients with infiltrated keratoses took nonsteroidal anti-inflammatory drugs twice as often as patients in the other groups, whereas those with lichen planus more frequently ingested antihypertensive drugs. Patients with erosive lichen planus were 10 times more likely to ingest nonsteroidal anti-inflammatory drugs than those with nonerosive lichen planus (p = 0.01).