Somatic health complaints are extremely common and are responsible for a large part of human suffering and healthcare costs. It has been recognised that psychosocial stress can affect somatic health. According to the 'perseverative cognition hypothesis', stressful events affect somatic health because people keep on worrying about them. Worry would prolong stress-related physiological activity that can ultimately lead to health problems. In this ambulatory study we tested whether stressful events and worry predict daily somatic complaints, and whether worry mediates the effects of stressful events. In addition, it was tested whether these effects were independent from negative affect. Using electronic diaries, 69 teachers (age 21-60 years) from Dutch primary and secondary schools reported daily stressful events, worry episodes, negative affect and somatic complaints for a period of 6 days. Results showed that worry intensity predicted the number of somatic complaints and mediated the effect of stressful events on somatic complaints. Furthermore, these results were independent from biobehavioural variables and daily negative affect. These findings support the perseverative cognition hypothesis proposing that the negative somatic health effects of stressful events are largely due to the worry; that is, to the prolonged cognitive representation of stressors.