Objective: We evaluated and compared the validity of patients' and rheumatologists' reports of infection with those confirmed by medical record review. Study Design and Setting: Reports of infections in 961 patients with rheumatoid arthritis from the Brigham and Women's Rheumatoid Arthritis Sequential Study (BRASS) were included over a 2-year period. BRASS is a longitudinal prospective cohort that collects detailed questionnaire data from patients semiannually and their treating rheumatologists every year. Results: Rheumatologist report of infection was more likely to be confirmed by medical record review than patient self-report (57.1% vs. 34.3% for definite or possible infections). Confirmation rates varied based on whether the participant received her primary care from the same network of health care providers. For participants with primary care "out of network," between 7.0% and 23.1% of patient or rheumatologist reports were confirmed by medical record review vs. between 16.1% and 41.7% for those with primary care "in network." Conclusion: The present study shows that relying strictly on patient or rheumatologist report of infection for a confirmed endpoint is not ideal but useful in case finding. The confirmation rate is affected by a number of factors including severity and definition of the infection and limited by data availability. © 2010 Published by Elsevier Inc. All rights reserved.