The purpose of this study was to determine whether exposure to stressful life events was associated with changes in levels of circulating cortisol during pregnancy in a population of 603 pregnant women. The participating pregnant women filled out a questionnaire and collected a morning and evening sample of saliva in early pregnancy (median 14th gestational week) and in late pregnancy (median and 30th gestational week). They were asked to report the number of life events experienced during first and second trimester, respectively, and were asked to rate the intensity of the experienced events. Complications related to the pregnancy such as vaginal bleeding and suspected growth retardation were registered and the women were asked about concerns about their pregnancy. The salivary samples were analyzed for cortisol and the levels were higher in late than in early pregnancy. In late pregnancy women exposed to more than one life event or were concerned about pregnancy complications during second trimester had a higher evening cortisol level, whereas morning values were unaffected. After adjustment for smoking women who experienced more than one very stressful life event had 27% higher evening cortisol concentrations (95% confidence intervals: 1-59%). Women with worries about pregnancy complications had 27% (95% confidence intervals: 2-57%) higher levels. In early pregnancy women reporting stressful life events did not have higher evening cortisol levels, but tended to have a blunted morning HPA response. In conclusion, we found differences in the associations between chronic stress in early and late pregnancy and cortisol levels indicating that the response to chronic stress is dependent on the stage of the pregnancy.