OBJECTIVES: The Rheumatoid Arthritis Disease Activity Index (RADAI) was developed to provide an easy to use self-administered assessment of rheumatoid arthritis (RA) to complement physician assessment.  This study evaluates the psychometric properties of a web administered version of the RADAI in a community sample in the US. METHODS: A random sample of iGuard.org members in the US treated with medications for RA completed the RADAI and a series of other questions related to their disease.  iGuard.org is a free medication monitoring service that is introduced to patients through multiple sources including physician, pharmacy and online referrals.  Internal consistency of the RADAI was evaluated using Cronbach’s alpha and item-total correlations, and factor analysis was used to confirm the domain structure.  Convergent validity was established using correlations with patient global assessment of pain and number of painful joints. RESULTS: A total of 153 RA patients completed the study.  The mean (SD) age of respondents was 52.7 (10.9) years, 71.2% were females with 54.3% diagnosed with RA 1 to 5 years ago and 39.2% diagnosed 5 to 15 years ago.  The mean (SD) RADAI score was 4.59 (2.16), patient global assessment of pain was 52.11 (24.88) on a 100-point scale, and number of painful joints were 7.93 (4.22).  RADAI items had good internal consistency with Cronbach’s alpha of 0.89 and all item-total correlations >=0.56.  Factor analysis confirmed one factor with factor loadings of all the items on the factor of >=0.57.  As expected, RADAI scores were significantly correlated with patient global assessment of pain (0.646; p<0.0001) and number of patient joints (0.649; p<0.0001). CONCLUSIONS: The study confirms the reliability and validity of a web administered version of the RADAI questionnaire in a US community sample.  It is a useful measure to assess RA disease status for patient recruitment in interventional studies and for observational study designs.