The present study attempted to replicate the robustness of a two-factor model of the Tampa Scale for Kinesiophobia (TSK) in chronic low back pain (CLBP) patients and fibromyalgia patients, by means of confirmatory factor analysis. Construct and predictive validity of the TSK subscales were also examined. Results clearly indicated that a two-factor model fitted best in both pain samples. These two factors were labelled somatic focus, which reflects the belief in underlying and serious medical problems, and activity avoidance, which reflects the belief that activity may result in (re)injury or increased pain. Construct validity of the TSK and its subscales was supported by moderate correlation coefficients with self-report measures of pain-related fear, pain catastrophising, and disability, predominantly in patients with CLBP. Predictive validity was supported by moderate correlation coefficients with performance on physical performance tests (i.e., lifting tasks, bicycle task) mainly in CLBP patients. Implications of the results are discussed and directions for future research are provided.