OBJECTIVE: Crohn's disease (aka: inflammatory bowel disease, regional enteritis) is a chronic autoimmune disorder that can occur at any age. This analysis examined use and cost of hospitalizations, observation unit (OU) stays and emergency department (ED) visits during a one-year period by patients with Crohn's disease. METHODS: Using 2001-2002 Massachusetts ED, OU and inpatient data, a cohort was identified by personal identifiers and ICD-9 principal diagnosis codes (555.0-555.9). An encounter profile was established for each patient starting with the first stay or visit at any hospital, ED or OU in Massachusetts in 2001. From that index encounter, each contact for regional enteritis was tracked for twelve months for that patient. Cost estimates, reported in 2004 USD, include accommodations and ancillary services. Charges were adjusted using a 0.55 cost-to-charge ratio and appropriate inflation indices. RESULTS: A cohort of 1553 patients was identified (females = 58%). The mean age was 43 years (range: <1-94 years). A total of 2459 encounters were identified during one year (mean encounters per patient = 1.6, range: 1-18) and 12% of patients used more than one location of care. Hospitalizations were 78%, ED visits were 18%, and OU stays were 4% of all encounters. On average, an inpatient stay was 5.6 days at a cost of $8354. Mean ED visit was five hours (average cost of $838). Mean OU stay was 28 hours (average cost of $2457). Cumulative cost for all inpatient, ED and OU encounters for these patients for one year was roughly $17.3 million and this is a conservative estimate of management costs, as it does not include physician, post-acute or usual outpatient care costs. CONCLUSIONS: These results show that managing this disorder requires use of resource intensive settings at a substantial cost and provide key information for health economic analyses of Crohn's disease.