Introduction Psychosocial factors at work are risk factors for several health outcomes, including musculoskeletal disorders such as low back pain (LBP). Few studies from high-income countries suggest a positive association between bullying at work and musculoskeletal pain, but the knowledge on this relationship is scarce. None studies on the theme are available from low- and middle-income countries.

Objectives Therefore, we aimed to investigate the association between workplace bullying and LBP in the last 7 days and chronic LBP in civil servants from a middle-income country.

Methods This is a cross-sectional study with 894 participants from judicial civil servants from a city in southern Brazil. Workplace Bullying was measured by the Negative Acts Questionnaire (NAQ-r) and Low Back Pain by the Nordic Questionnaire for Musculoskeletal Symptoms (NQMS). Logistic Regression was used to analyse data and test hypotheses, estimating prevalence odds ratios (POR).

Results The prevalence of workplace bullying was 18.2%. The overall prevalence of LBP in the last 7 days was 50.1%, and of Chronic LBP was 19.3%. Psychosocial factors at work such as occupational stress were strongly associated with both outcomes. Workplace bullying was strongly associated with LBP, even after adjustment for several confounders. The risk of LBP in the last 7 days among bullied workers was 89.0% higher (POR=1.89; 95%CI: 1.31–2.71), compared to non-bullied employees. Bullying was also associated with chronic LBP after adjustment for sociodemographic, behavioural and some occupational factors (POR=1.60; 95% CI: 1.05–2.44).

Conclusions Psychosocial factors at work, particularly workplace bullying, were strong risk factors for LBP, in contrast to most individual factors. Dose-response patterns were showed. Positive associations between bullying and LBP raise hypotheses on causation, emphasising the role of bullying as an important psychosocial risk at work. Further longitudinal studies should address these hypotheses, investigating mechanisms, effect modification and possible mediation.