Background. Many women suffer from health problems after giving birth, which can lead to sick leave. About 30% of Dutch workers are on sick leave after maternity leave. Structural contact of supervisors with employees on maternity leave, supported by early medical advice of occupational physicians, may increase the chances of return-to-work after maternity leave. In addition, to understand the process of sick leave and return-to-work after childbirth it is important to gain insight into which factors hinder return-to-work after childbirth, as well, as which prognostic factors lead to the development of postpartum health complaints. In this paper, the design of the Mom@Work study is described. Methods. The Mom@Work study is simultaneously a randomised controlled trial and a cohort study. Pregnant women working for at least 12 hours a week at one of the 15 participating companies are eligible to participate. The supervisors of these pregnant employees are randomised at 35 weeks pregnancy into the intervention group or control group. During maternity leave, supervisors in the intervention group contact their employee six weeks after delivery using a structured interview. When employees do not expect to return to their jobs at the end of their scheduled maternity leave due to health problems, the supervisor offers early support of the occupational physician. Supervisors in the control group have no structural contact with their employees during maternity leave. Measurements take place at 30 weeks pregnancy and at 6, 12, 24 and 52 weeks postpartum. In addition, cost data are collected. For the RCT, primary outcome measures are sick leave and return-to-work, and secondary outcome measures are costs, health, satisfaction with intervention and global feelings of recovery. Outcome measures for the cohort are pregnancy-related pelvic girdle pain, fatigue and depression. Finally, a number of prognostic factors for return-to-work and for the development of complaints will be measured. Discussion. The Mom@Work study will provide important information about return-to-work of employees after giving birth. Results will give insight in prognosis of postpartum sick leave and complaints. Also, the role of supervisors and occupational physicians in successful return-to-work after childbirth will be clarified. © 2007 Stomp-van den Berg et al; licensee BioMed Central Ltd.