Pain-related fear and avoidance of physical activities are central elements of the fear-avoidance model of musculoskeletal pain. Pain-related fear has typically been measured by self-report instruments. In this study, we developed and validated a Behavioral Avoidance Test (BAT) for chronic low back pain (CLBP) patients with the aim of assessing pain-related avoidance behavior by direct observation. The BAT-Back was administered to a group of CLBP patients (N=97) and pain-free controls (N=31). Furthermore, pain, pain-related fear, disability, catastrophizing, and avoidance behavior were measured using self-report instruments. Reliability was assessed with intraclass correlation coefficient and Cronbach α. Validity was assessed by examining correlation and regression analysis. The intraclass correlation coefficient for the BAT-Back avoidance score was r=0.76. Internal consistency was α=0.95. CLBP patients and controls differed significantly on BAT-Back avoidance scores as well as self-report measures. BAT-Back avoidance scores were significantly correlated with scores on each of the self-report measures (rs=0.27 to 0.54). They were not significantly correlated with general anxiety and depression, age, body mass index, and pain duration. The BAT-Back avoidance score was able to capture unique variance in disability after controlling for other variables (eg, pain intensity and pain-related fear). Results indicate that the BAT-Back is a reliable and valid measure of pain-related avoidance behavior. It may be useful for clinicians in tailoring treatments for chronic pain as well as an outcome measure for exposure treatments.