Stress-related illnesses, such as mental, behavioral, and cardiovascular diseases, are common causes for sick-leave absences. It is generally assumed that burnout, the chronic stress syndrome, also leads to absenteeism and poor health, but this assumption has rarely been tested. The authors investigated the prospective effect of burnout on registered sick leaves and their causes in industrial employees. We collected the number of medically certified (> 3 days) absence episodes and their causes (according to the International Statistical Classification of Diseases-10 diagnostic categories) of 3,895 industrial employees from a company register during 1995 to 1998. Burnout was measured in 1996 with the Maslach Burnout Inventory-General Survey, which defines burnout as a 3-dimensional syndrome consisting of components of exhaustion, cynicism, and lack of professional efficacy. In Poisson regression models, the total burnout score increased the risk for future all-cause absences after adjustment for age, sex, occupation, and baseline absence. Burnout increased the risk of future absences because of mental and behavioral disorders, diseases of the circulatory system, diseases of the respiratory system, and diseases of the musculoskeletal system. Of the separate components of burnout, exhaustion was strongly related to future diseases of the circulatory system, whereas cynicism was strongly related to future diseases of the digestive system. Other differentiated effects were also found. The results of this study show that burnout is related to increased risk of future illness. This implies that burnout prevention can reduce future absenteeism and has a major economic impact on work life and health care.