Objectives: To identify signs and symptoms that should alert clinicians to the need for additional psychological assessment in patients with chronic low back pain (CLBP). Methods: In this prospective cohort study, 229 consecutive patients with CLBP who attended an outpatient rehabilitation center were assessed by psychologists and physical therapists before their treatment started. The signs and symptoms assessed by the physical therapists were compared with the assessments made by the psychologists, which were considered to be the reference standard (relevant psychological disturbances, yes or no). Univariable and multivariable regression methods were applied to investigate which signs and symptoms were associated with the reference standard. A receiver operator characteristic (ROC) curve was constructed to assess the overall accuracy of the final model. Results: The psychologists classified 53% of the patients as having relevant psychological disturbances. Univariable analysis revealed statistically significant differences (P<0.05) between the 2 patient groups (relevant psychological disturbances, yes or no) for 10 of the 17 signs and symptoms. Multivariate analysis yielded a screening instrument consisting of the following 4 signs and symptoms: presence of Waddell signs, elevated scores on the pain drawing, absence of a directional preference, and daily use of analgesic medication for CLBP [area under the ROC curve, 0.81 (95% confidence interval: 0.75, 0.87)]. Discussion: This study established a clinically useful screening instrument for the identification of patients with CLBP who might benefit from additional psychological assessment in an outpatient rehabilitation setting. Further research is needed to confirm our preliminary results. Copyright © 2011 by Lippincott Williams & Wilkins.