BACKGROUND: Patients receiving 5-aminosalicylic acid (5-ASA) require long-term therapy to achieve good outcomes. Persistency (duration of time from initiation to discontinuation of therapy) is therefore an important consideration. AIM: To evaluate persistency in patients receiving various oral 5-ASA formulations. METHODS: This retrospective, 12-month, cohort study examined new-starter patients (any age and diagnosis) from a large United States pharmacy database who filled a prescription for oral 5-ASA [Lialda((R)), Asacol((R)), Pentasa((R)) 250 or 500 mg, balsalazide (generic and Colazal((R))), and olsalazine (Dipentum((R)))] between March and September 2007. Persistency was evaluated monthly on the basis of prescription refill rates. RESULTS: Prescription and refill records were identified for 44,191 patients receiving oral 5-ASA. After 1 year, 20% of patients receiving Lialda were considered persistent and classified as continuing (refilling within a timeframe of up to twice the duration of the prescription), compared with 9% receiving Asacol, 7 (250 mg) and 10% (500 mg) receiving Pentasa, 10% receiving balsalazide, and 10% receiving Dipentum. CONCLUSIONS: Overall persistency with oral 5-ASA therapy was low. However, patients receiving once-daily Lialda had significantly higher persistency after 1 year of treatment than patients receiving other oral 5-ASA therapies.