After the procedure, you will start taking celecoxib by mouth once every 12 hours for 6 months. You will also have around 1 teaspoon of blood drawn to measure the amount of celecoxib in your blood at the completion of month 2 and 4 of celecoxib treatment. At the end of the 6 month treatment period, you will have another colonoscopy procedure. This is an additional procedure performed solely for this study and is not part of your standard of care for the treatment of familial adenomatous polyposis. A second set of biopsies will be taken (23 maximum). These biopsy samples will be studied and compared to the samples taken before treatment with celecoxib. You will also have around 1 teaspoon of blood drawn to measure the amount of celecoxib in your blood.