OBJECTIVES: Prior research evaluated the impact of infliximab (IFX) adherence on resource use and costs in Crohn’s disease (CD).  Purpose was to examine the association between adherence and all-cause healthcare costs among those who are treated with IFX for inflammatory bowel disease (IBD). METHODS: Patients with >1 claims for IFX initiated between January 1, 2006 to December 31, 2009 who had >2 IBD diagnoses of Crohn’s disease (CD; ICD-9-CM: 555.XX) or ulcerative colitis (UC; ICD-9-CM: 556.XX) during the pre-index period were identified from Thomson Reuters Marketscan® Databases.  Patients had to be >18 years, continuously enrolled for 12 months before and after IFX initiation, and had no prior use of IFX during 360-days pre-index.  Patients with prior biologic therapy or rheumatoid arthritis (ICD-9-CM: 714.XX) were excluded.  Adherent group was classified as having a medication possession ratio (MPR) of >80%; non-adherent group had an MPR<80%.  Differences between the adherent and non-adherent groups were assessed using propensity-weighted general linear models. RESULTS: A total of 1,646 IBD patients were identified (945 CD; 701 UC) with a mean (SD) age of 44.4 (15.6) and 48.3% were female.  Of these, 41% were adherent and 59% were non-adherent.  Propensity-weighted mean total healthcare costs excluding IFX were $13,424 vs. $32,522 (P<0.0001) for the adherent vs. non-adherent groups.  Mean all-cause component costs were $2,458 vs. $17,634 (P<0.0001) for hospitalizations, $7,357 vs. $10,909 (P<0.0001) for outpatient visits, and $236 vs. $458 (P<0.0001) for ER visits in the adherent vs. non-adherent groups, respectively; total costs (component+ IFX) were also significantly lower in the adherent group.  No significant differences were observed in other prescription costs. CONCLUSIONS: Medication adherence was associated with significantly lower total healthcare costs in patients treated with IFX for IBD.  These differences may be explained by reduced hospitalization, outpatient, and ER costs observed in the adherent vs. non-adherent groups.