BACKGROUND: Common mental disorders are important contributors to the global burden of disease and cause negative effects on both the individual and society. Stress-related disorders influence the individual's workability and cause early retirement pensions in Denmark. There is no clear evidence that mental health care alone will provide sufficient support for vocational recovery for this group. Integrated vocational and health care services have shown good effects on return to work in other similar welfare contexts. The purpose of the Danish IBBIS (Integreret Behandlings- og BeskæftigelsesIndsats til Sygemeldte) study is to examine the efficacy of (1) a stepped mental health care intervention with individual stress coaching and/or group-based MBSR and (2) an integrated stepped mental health care with individual stress coaching and/or group-based MBSR and vocational rehabilitation intervention for people on sick leave because of exhaustion disorder, adjustment disorder or distress in Denmark. METHOD/DESIGN: This three-armed, parallel-group, randomized superiority trial is set up to investigate the effectiveness of a stepped mental health care intervention and an integrated mental health care and vocational rehabilitation intervention for people on sick leave because of exhaustion disorder, adjustment disorder or distress in Denmark. The trial has an investigator-initiated multicenter design. Six hundred and three patients will be recruited from Danish vocational rehabilitation centers in four municipalities and randomly assigned into three groups: (1) IBBIS mental health care integrated with IBBIS vocational rehabilitation, (2) IBBIS mental health care and standard vocational rehabilitation, and (3) standard mental health care and standard vocational rehabilitation. The primary outcome is register-based return to work at 12 months. The secondary outcome measures are self-assessed level of depression (BDI), anxiety (BAI), distress symptoms (4DSQ), work- and social functioning (WSAS), and register-based recurrent sickness absence. DISCUSSION: This study will contribute with knowledge on the consequence of the current organizational separation of health care interventions and vocational rehabilitation regarding the individual's process of returning to work after sick leave because of exhaustion disorder, adjustment disorder or distress. If the effect on return to work, symptom level, and recurrent sick leave is different in the intervention groups, this study can contribute with new knowledge on shared care models and the potential for preventing deterioration in stress symptoms, prolonged sick leave, and recurrent sick leave. TRIAL REGISTRATION: ClinicalTrials.gov, registration number: NCT02885519 . Retrospectively registered on 15 August 2016). Participants have been included in the IBBIS trial for distress, adjustment disorder and exhaustion disorder since April 2016.