UNASSIGNED : The Fear-Avoidance Belief Questionnaire for physical activity (FABQ-PA) was originally developed for patients with low-back pain. Whether the FABQ-PA is suitable for use among patients with other musculoskeletal disorders has been sparsely evaluated. UNASSIGNED : To evaluate test-retest reliability, measurement error, construct validity, and responsiveness of the FABQ-PA in patients with shoulder impingement syndrome (SIS). UNASSIGNED : This prospective cohort study included 45 patients with SIS. Data were collected with questionnaires at baseline, after 2-4 days, and at 3 months, which included the Danish versions of the FABQ-PA and the Oxford Shoulder Score (OSS). Test-retest reliability was assessed by intraclass correlation, and standard error of measurement was estimated and converted into the minimal detectable change (MDC). Construct validity was investigated by analyzing the correlation between the baseline scores of the FABQ-PA and the OSS. Responsiveness was investigated from longitudinal construct validity using a correlation analysis reflecting changes over time. UNASSIGNED : Test-retest reliability showed an intraclass correlation of 0.80, and examination of the measurement error showed no systematic differences and a MDC of 7.95 (95% CI 6.57-10.07). Construct validity showed a correlation of -0.60 (95% CI -0.76 to -0.37) between the FABQ-PA and OSS at baseline. A weaker correlation between FABQ-PA- and OSS-change scores was observed (-0.43, 95% CI -0.67 to -0.12). UNASSIGNED : The Danish version of the FABQ-PA is suitable for assessing fear-avoidance beliefs in groups of patients with SIS, but its ability to evaluate individual patients and changes over time may be more limited.