In a population-based sample, the authors examined the validity of preeclampsia and related diagnoses recorded in a mandatory Danish national hospital discharge registry and in a standardized telephone interview of women who gave birth between 1998 and 2002. Using a "gold standard" for preeclampsia defined in accordance with the guidelines from the American College of Obstetricians and Gynecologists, the authors reviewed hospital charts of 3,039 women and found that 61of 88 preeclampsia cases (69.3%) and 24 of 55 cases of serious subtypes of preeclampsia (43.6%) were recorded as such by the registry. A total of 21 of 2,951 women without preeclampsia (0.71%) had a preeclampsia diagnosis in the registry. All registrations of serious subtypes of preeclampsia reflected true cases. The positive predictive value of a preeclampsia diagnosis in the registry was 74.4%. Including interview data reduced the sample size to 2,307 women. In this sample, of 62 women with preeclampsia, 45 (72.6%) reported in the interview to have had preeclampsia. Of 2,245 women with no preeclampsia, 31 (1.4%) reported to have had preeclampsia. The positive predictive value of the women's own report on preeclampsia was 59.2%. The authors conclude, for the purpose of etiologic studies, that the registry had acceptable validity, whereas the usefulness of self-reported information may be limited.