The Manitoba Early Arthritis Cohort is an expanding inception cohort of adult patients with early inflammatory arthritis defined as symptom duration ≤ 12 months and at least one inflamed joint(n>350; RA or undifferentiated arthritis ≈80%. The cohort was established in 2000. Detailed demographic information is obtained on entry and updated annually. ACR diagnosis, medical co-morbidities (Charlson co-morbidity index (modified for outpatient use)and patient self-report, patient reported quality of life indices (SF-36v2, EQ-5D), self reported use of health care resources, work status, and radiographs are obtained annually. Detailed arthritis specific clinical information including measures of disease activity (active joint counts; ESR; CRP) and functional status (mHAQ) are obtained at each visit. Routine investigations, including arthritis related serology (RF, CCP2), arthritis related medications and reasons for changing medications are recorded. Treatment is at the discretion of the attending rheumatologist but collaborating rheumatologists follow current guidelines for treating early RA and generally treat with aim for disease remission. All patients consent prior to enrolling in the cohort. The cohort and related research have been approved by the local Health Research Ethics Board.