Rationale, aims and objectives: We aimed to investigate whether a quality improvement initiative, implementing evidence-based return-to-work (RTW) services in a Danish job center, could reduce the duration of sick leave and increase self-reported outcomes in citizens on sick leave due to back pain. Method: The study was a quality improvement (QI) study, conducted in a large municipality, using a quasi-experimental prospective design. Citizens receiving sickness benefits due to back pain were allocated either to a department providing RTW services as usual or to the QI department. The QI intervention included earlier timing of contact with citizens, integrated collaboration between case managers and physiotherapists, and workplace involvement in the RTW process. The QI intervention was evaluated by measuring citizens’ rate of RTW, and their self-reported disability, self-efficacy for RTW and fear-avoidance beliefs. Follow-up varied from 3 to 15 months. Results: 324 citizens were included, of which 134 were allocated to the QI group. Sociodemographic characteristics of the QI and control groups were similar at baseline. No difference was seen on rate of RTW, with a hazard ratio of 0.95 (P = 0.741). For self-reported outcomes, the QI group reported significantly higher self-efficacy for RTW (P = 0.030), while there were no differences between groups on disability and fear-avoidance beliefs. Conclusions: The implementation of evidence-based practice in RTW-services for citizens on sick leave due to back pain in a Danish setting, did not have an effect on the rate of RTW, probably because the workplace involvement and close collaboration between physiotherapists and case managers at the job center had limited implementation success. However, self-efficacy for RTW was significantly higher in the QI group compared to the control group. The findings were confirmed in a per protocol analysis.