BackgroundSubgrouping patients with chronic low back pain is recommended prior to selecting treatment strategy, and fear avoidance beliefs is a commonly addressed psychological factor used to help this subgrouping. The results of the predictive value of fear avoidance beliefs in patients with chronic low back pain in prognostic studies are, however, not in concordance. Therefore, the objective of this study was to examine the association between fear avoidance beliefs at baseline and unsuccessful outcome on sick leave, disability and pain at 12-month follow-up in patients with entirely chronic low back pain.MethodsA secondary analysis of data from a randomised controlled trial. Patients with chronic low back pain (n = 559) completed questionnaires at baseline and after 12 months. Multiple logistic regression analyses were conducted to examine the association between fear avoidance beliefs and the outcomes sick leave, disability and pain.ResultsHigher fear avoidance beliefs about work at baseline were found to be significantly associated with still being on sick leave (OR 1.11; 95% CI 1.02–1.20) and having no reduction in pain (OR 1.04; 95% CI 1.01–1.08) after 12 months and may be associated with having no reduction in disability (OR 1.03; 95% CI 1.00–1.06) after 12 months (lower limit of 95% CI close to 1.00). Fear avoidance beliefs about physical activity were not found to be associated with the three outcomes.ConclusionsHigh fear avoidance beliefs about work are associated with continuous sick leave after 1 year in patients with chronic low back pain. This finding might assist clinicians in choosing targeted treatment strategies in subgroups of working patients with chronic low back pain.Electronic supplementary materialThe online version of this article (10.1186/s12891-018-2351-9) contains supplementary material, which is available to authorized users.