BACKGROUND: A woman's dissatisfaction with the experience of labor and birth may affect her emotional well-being and willingness to have another baby. The aim of this study was to investigate the prevalence and risk factors of a negative birth experience in a national sample. METHODS: A longitudinal cohort study of 2541 women recruited from all antenatal clinics in Sweden during 3 weeks spread over 1 year was conducted. Data were collected by three questionnaires, which measured women's global experience of labor and birth 1 year after the birth, and obtained information on possible risk factors during pregnancy and 2 months after the birth. RESULTS: Seven percent of the women had a negative birth experience. The following risk factors were found: (1) factors related to unexpected medical problems, such as emergency operative delivery, induction, augmentation of labor, and infant transfer to neonatal care; (2) factors related to the woman's social life, such as unwanted pregnancy and lack of support from partner; (3) factors related to the woman's feelings during labor, such as pain and lack of control; and (4) factors that may be easier to influence by the caregivers, such as insufficient time allocated to the woman's own questions at antenatal checkups, lack of support during labor, and administration of obstetric analgesia. CONCLUSIONS: Many risk factors were related to unexpected medical problems and participants' social background. Of the established methods to improve women's birth experience, childbirth education and obstetric analgesia seemed to be less effective, whereas support in labor and listening to the woman's own issues may be underestimated.