The association between women's overall experience of labor and birth and a range of possible explanatory variables were studied in a group of 1111 women who participated in a birth center trial. Data were collected by a questionnaire in early pregnancy (demographic background, parity, personality traits, and expectations), hospital records (pharmacological pain relief, induction, augmentation of labor, duration of labor, operative delivery, and infant outcome), and a follow-up questionnaire 2 months after the birth (the principal outcome "overall experience of labor and birth," pain, anxiety, freedom in expression, involvement, midwife, and partner support). Logistic regression was conducted by including all variables that were associated with the birth experience when analyzed one by one. In a second regression analysis, only explanatory variables measured independently of the principal outcome were included; that is, only data collected from the pregnancy questionnaire and the hospital records. The first regression analysis identified five explanatory variables: involvement in the birth process (perceived control) and midwife support were associated with a positive experience; anxiety, pain, and having a first baby with a negative experience. Parity remained a significant predictor in the second regression analysis, but the others were replaced by augmentation of labor, cesarean section, instrumental vaginal delivery, and nitrous oxide (Entonox), which were all associated with a negative birth experience.