After colectomy with ileorectal anastomosis (IRA) for treatment of familial adenomatous polyposis (FAP), the rectal mucosa remains, with the risk of malignant change. Locoregional (rectal) sulindac has been applied, with initial higher-dose therapy and subsequent low-dose maintenance therapy to minimise side-effects. The dose-finding study with sulindac suppositories started with a dose of 300 mg sulindac daily per patient over 6 weeks. Depending on proctoscopical evaluation of regression of polyposis, sulindac doses were reduced in predefined steps. Ten of 15 patients developed a complete remission following 42 weeks of treatment, while the rest had partial remission. Responses were recorded 6-24 weeks after beginning sulindac treatment. After 36 weeks, 13/15 patients received 25-50 mg sulindac daily. An increase in the number of partial remissions after 42 weeks of treatment at doses of 100 mg sulindac daily may indicate the first approach to a reduced dose between 100 mg to 25 mg sulindac daily, but may also point to the importance of long-term treatment rather than dose-intense therapy.