Thiopurines are widely used for remission maintenance and post-operative recurrence prevention in Crohn's disease. The increased risk of cancer in transplant recipients on azathioprine is well recognized and there are concerns that this may also be true for inflammatory bowel disease patients. We report a case of a 33-year-old Caucasian woman with Crohn's disease treated with azathioprine for 9 years who developed an ulcerated lesion at the right superior retromolar trigone. Biopsy specimen revealed a squamous cell carcinoma.