Background The extensive Dutch occupational health care system of the past decade has not led to the desired outcomes, namely, a decrease of work absenteeism and the associated costs. Aim To assess the differences between in-house and external occupational health care services in the process quality of occupational health care provided. Methods In total, 26 interviews were conducted with chief executive officers of occupational health services (OHS). The responses and other relevant policy documents were analysed and described. A key component of this process was to compare differences between in-house and external services. Results Notable differences in quality were found to exist between in-house and external occupational health care systems, with the in-house occupational health care services offering the highest process quality. Conclusion Our findings suggest that the effectiveness of OHS is mainly dependent on their structure (in-house versus external) and on economic factors (profit driven versus not for profit).