objective activity data to determine whether patients with chronic lower back pain report their activity levels as accurately as controls do. DESIGN: A cross-sectional study was performed in patients and controls. SETTING: The study was carried out in the daily environment of the subjects. SUBJECTS: Thirty-two chronic lower back pain patients with symptoms more than three months and 20 healthy controls from the Netherlands, aged 18-65 years. MAIN MEASURES: A tri-axial accelerometer was worn for five weekdays