OBJECTIVES: To evaluate the impact of persistence with infliximab treatment on medical costs among patients with Crohn's disease (CD), using a managed care database. METHODS: A retrospective study using the PharMetrics managed care plan database in the US from July 1, 1999 through June 30, 2005 was conducted. Patients newly initiated on infliximab, continuously enrolled for 12 months before and after their index infliximab claim, and having at least two diagnoses of CD (one of which occurring in the pre-index period) were included. Persistence (%) was defined as the number of days between the first infliximab claim and the last infliximab encounter, divided by 365 and multiplied by 100. Two mutually exclusive cohorts were defined based on the levels of infliximab persistence: patients who were persistent >=80% and those who were persistent <80%. CD-related medical costs (those in which CD was the diagnosis) in the 12-month post-index period were computed for each patient. The cost of adverse events could not be identified separately in this analysis. Univariate differences between the persistent and non-persistent cohorts were assessed using Mann-Whitney and chi-square tests. RESULTS: Four hundred, eighty patients were included, 251 (52.29%) with a persistency ratio >=80% and 229 (47.71%) with a persistency ratio <80%; 55% were female and the mean age was 36.9 years. The 80% persistency cohort had lower CD-related medical costs compared with the <80% persistency cohort ($4380.21 versus $8570.11; p=ns), primarily driven by inpatient costs ($2014.31 versus $5981.51; p<0.001). Costs were also higher for emergency room and outpatient levels of care in the lower persistency cohort. CONCLUSION: This study indicates that a higher persistence rate with infliximab therapy is associated with lower CD-related medical costs, primarily driven by decreased inpatient hospital costs. Future studies to examine the impact of persistence with infliximab on clinical and humanistic outcomes are recommended.