Epidural analgesia is used by more than half of laboring women, yet there is no consensus about what unintended effects it causes. To evaluate the state of our knowledge, we performed a systematic review of the literature examining the unintended maternal, fetal, and neonatal effects of epidural analgesia used for pain relief in labor by low-risk women. Our review included randomized and observational studies appearing in peer review journals since 1980. Much of the evidence is equivocal. Existing randomized trials are either small or do not allow clear interpretation of the data because of problems with protocol compliance. In addition, few observational studies control for the confounding factors that result because women who request epidural are different from women who do not. There is considerable variation in the association of epidural with some outcomes, particularly those that are heavily practice-based. Despite this variation, there is sufficient evidence to conclude that epidural is associated with a lower rate of spontaneous vaginal delivery, a higher rate of instrumental vaginal delivery and longer labors, particularly in nulliparous women. Women receiving epidural are also more likely to have intrapartum fever and their infants are more likely to be evaluated and treated for suspected sepsis. There is insufficient evidence to determine whether epidural does or does not tend to increase the risk of cesarean delivery or fetal malposition. Adverse effects on the fetus may occur in the subset of women who are febrile. Women should be informed of unintended effects of epidural clearly supported by the evidence, especially since epidural use is almost always an elective procedure. Further research is needed to advance our understanding of the unintended effects of epidural. Improved information would permit women to make truly informed decisions about the use of pain relief during labor.