Objectives The International Physical Activity Questionnaire Short Form (IPAQ-SF) is a self-report questionnaire commonly used in patients with rheumatoid arthritis (RA) to measure physical activity. However, despite its frequent use in patients with RA, its validity has not been ascertained in this population. The aim of this study was to examine the criterion validity of energy expenditure from physical activity recorded with the IPAQ-SF in patients with RA compared with the objective criterion measure, the Sense Wear Armband (SWA) which has been validated previously in this population.Design Cross-sectional criterion validation study.Setting Regional hospital outpatient setting.Participants Twenty-two patients with RA attending outpatient rheumatology clinics.Interventions Subjects wore an SWA for 7 full consecutive days and completed the IPAQ-SF.Main outcome measures Energy expenditure from physical activity recorded by the SWA and the IPAQ-SF.Results Energy expenditure from physical activity recorded by the IPAQ-SF and the SWA showed a small, non-significant correlation (r = 0.407, P = 0.60). The IPAQ-SF underestimated energy expenditure from physical activity by 41% compared with the SWA. This was corroborated using Bland and Altman plots, as the IPAQ-SF was found to overestimate energy expenditure from physical activity in nine of the 22 individuals, and underestimate energy expenditure from physical activity in the remaining 13 individuals.Conclusion The IPAQ-SF has limited use as an accurate and absolute measure for estimating energy expenditure from physical activity in patients with RA. (C) 2014 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.