BACKGROUND CONTEXT: Ten percent of patients with low back pain (LBP) are not able to resume work within 3 months of sick leave, accounting for 90% of all medical and indemnity costs. PURPOSE: To quantify the relative contribution of sociodemographic, clinical, occupational, and psychological risk factors in determining the non-return to work after 3 months of compensated LBP and to develop a screening tool to identify patients who require further guidance and rehabilitation. STUDY DESIGN/ SETTING: A 6-month prospective cohort study of disabled workers applying for compensation benefit because of LBP during a 6-month period in the Belgian compulsory health insurance system. PATIENT SAMPLE: Three hundred and forty-six patients. OUTCOME MEASURES: Patients unable to resume work within 3 months of sick leave were classified as bad outcomes. METHODS: Consecutively, injured workers applying for income replacement benefits between October 2003 and March 2004 because of LBP were followed 6 months after the start of the sick leave period. All subjects underwent a standardized physical examination and completed a battery of 12 self-report questionnaires. RESULTS: Forty-seven percent of the population had not resumed work 3 months after the start of the sick leave period. The risk factors for sickness absence more than 3 months were Oswestry disability index (odds ratio for each point increase: 1.04; 95% confidence interval: 1.02-1.06), fear of avoidance severity score (odds ratio for each point increase: 1.05; confidence interval: 1.02-1.09), blue collar worker (odds ratio: 2.18; confidence interval: 1.21-3.92), LBP for less than 12 weeks before sick leave (odds ratio: 0.32; confidence interval: 0.17-0.64), and pain behavior (odds ratio for each point increase: 1.72; confidence interval: 1.25-2.39). A multivariate screening test based on five questions identified 80% of the patients unable to resume work after 3 months of sick leave (specificity: 56.6; cut off: 0.4). CONCLUSIONS: A questionnaire comprising a limited set of items allows a practical screening of LBP patients unlikely to resume work.