OBJECTIVES: Assess risk factors associated with nonpersistence/nonadherence to oral 5-aminosalicylic acid (5-ASA) medications in ulcerative colitis (UC) patients. METHODS: IMS LifeLink™ Health Plan claims data 2007-2011 were analyzed to identify patients ≥18 years with ≥1 UC diagnosis (ICD-9-CM: 556.x) and had ≥1 prescription for 5-ASA [balsalazide disodium, mesalamine delayed release, Multi-Matrix System mesalamine (MMX), sulfasalazine] during the study period.  5-ASA Medications nonpersistence/nonadherence following 12 months initial prescription fill (index medication) were evaluated.  Nonpersistence with index medication was assessed for discontinuation (gap ≥60 days).  Switch was identified if patients changed to another product after discontinuing the index medication.  Nonadherence was determined by medication possession ratio (MPR) <0.8 for index medication, and proportion of days covered (PDC) <0.8 for any 5-ASA.  Cox model assessed relative hazards associated with discontinuation.  Logistic regression investigated risk factors associated with nonadherence (PDC<0.8). RESULTS: A total of 7608 patients met selection criteria.  The median days to discontinuation differed significantly across index medications (range, 97 [sulfasalazine] to 175 days [MMX], P<0.0001).  Patients on MMX were less likely to discontinue (75.3% vs ≥80.8%, P<0.0001), or switch (9.9% vs. ≥12%, P=0.01), and more likely to adhere to their medications (MPR≥0.8; 24.1% vs. ≤18.0%, P<0.0001) than those on other medications.  Major predictors of nonpersistence included index medication vs MMX (balsalazide disodium: HR=1.18; mesalamine delayed release: HR=1.23; sulfasalazine: HR=1.44), preferred provider organization (PPO) vs health maintenance organization (HR=1.10), and no prior use of immunosuppressive agents (HR=1.26).  Significant variables associated with nonadherence included not switching medication (OR=2.03), residing in South versus Midwest region (OR=1.42), never receiving specialist care (OR=1.34), and Medicaid/Medicare versus commercial plan (OR=1.44). CONCLUSIONS: Patients on once-daily MMX had the lowest risk of discontinuation and the highest adherence rate.  Multiple factors including not using immunosuppressive agents, residing in South region, PPO plan, and non-commercial payer were associated with nonpersistence/nonadherence with 5-ASAs.