Objective: Several biologics, especially TNF antagonists, have been established as effective therapy for Crohn's disease (CD). Adherence to biologic therapy is thought to be important for optimal outcomes. This analysis retrospectively quantified the impact of non-adherence to infliximab maintenance therapy on medical service use by CD patients. Methods: CD patients on infliximab maintenance therapy were identified from the Integrated Healthcare Information Services claims database (covering approximately 35 million managed care lives from January 1, 1999 to June 30, 2006) if they had =4 infliximab infusions (with intervals =12 weeks between the first four infusions) in the first year following infliximab initiation. Non-adherence was defined as total number of infliximab infusions <7 in the first year (the expected number is =8 if patients follow the labeled schedule). One-year medical service utilization and costs (excluding infliximab drug/administration costs) were analyzed. Descriptive statistics and multivariate regressions adjusted for confounders were performed. Results: A total of 647 CD patients were identified. The 1-year non-adherence rate was 35.9%. Descriptive statistics demonstrated that non-adherent patients were more frequently hospitalized, and incurred greater 1-year costs for hospitalization and total medical services (p=0.05 for all comparisons). Adjusted multivariate regression analyses demonstrated that, compared with adherent patients, non-adherent patients had greater risks of hospitalization (odds ratios were 2.3 for CD-related; 2.5 for all-cause, both p<0.001); and incurred greater costs for hospitalization (additional $7767 for CD-related, $9417 for all-cause; both p=0.001), outpatient visits (additional $1025 for CD-related, p<0.001; $1,307 for all-cause, p=0.003), and total medical services (additional $5236 for CD-related and $6953 for all-cause, both p<0.001). Conclusion: More than one-third of the CD patients on infliximab maintenance therapy in the cohort were non-adherent to therapy within 1 year. Non-adherence was associated with greater medical service utilization and costs.