['Non-adherence to 5-aminosalicylic acid (5-ASA) is associated with adverse outcomes; however, no data exist regarding cost and non-adherence. Our aim was to determine the association between adherence to maintenance therapy and healthcare costs.', 'Patients in the Maryland CareFirst BlueCross BlueShield program with a follow-up of more than 1 month who had been prescribed at least one 5-ASA preparation during the period 1 January 2002 to 31 December 2004 were included. Non-adherence was defined as failure to refill a prescription claim, and a medication possession ratio was calculated. Generalized linear models were built to determine the association between annual average cost per patient.', 'A total of 4313 patients were included, although only 57% were adherent with their index medication. The mean medication possession ratio ranged from 72% for Azulfidine to 82% for generic sulfasalazine. A twofold difference in gastroenterology-related inpatient cost in non-adherent versus adherent patients (22.8% vs 11.7%, P < 0.01) was observed. Non-adherence also incurred more costs for outpatient services and office visits. In multivariate analysis, patients who were persistent with their medications incurred 12.5% lower medical costs (P = 0.03).'] Is medication non-adherence associated with increased medical health care costs?