This article summarizes arguments for building an evidence base for occupational health. Evidence is needed on the most effective ways of eliminating health hazards in the workplace and at work, enhancing healthy behavior or the empowerment of workers, and preventing and treating occupational diseases and occupational disability. An evidence base for occupational health must include systematic reviews. The Cochrane Collaboration has brought together some of the evidence; however, a search for systematic reviews on the top priorities in occupational health research showed that systematic reviews are lacking in many areas. Current reviewing methods can be adapted to the special features of occupational health. It is concluded that more effort should be invested in the preparation, maintenance, and dissemination of systematic reviews in order to create a necessary evidence base for occupational health intervention. Occupational health could benefit considerably from greater awareness of the evidence for and against various types of intervention.