Studies in Britain point to a rise in the incidence of intra-oral cancer in the last 20 years, paralleling trends evident in other European countries. Cases of histologically-diagnosed primary intra-oral squamous cell carcinoma have been ascertained by reviewing the records of pathology departments in Northern Ireland. Trends in the incidence of the disease have been determined for the period 1975-89. There has been a significant increase in the incidence among men, rising from 1.78 to 3.14 per 100,000. In women over the same period the incidence rose from 0.87 to 1.19 per 100,000, but this change was not significant. These trends concur with recent findings from other countries.