The professional literature on the benefits and risks of episiotomy was last reviewed critically in 1983, encompassing material published through 1980. This paper reviews the evidence accumulated since then. (Part II follows in this issue.) It is concluded that episiotomies prevent anterior perineal lacerations (which carry minimal morbidity), but fail to accomplish any of the other maternal or fetal benefits traditionally ascribed, including prevention of perineal damage and its sequelae, prevention of pelvic floor relaxation and its sequelae, and protection of the newborn from either intracranial hemorrhage or intrapartum asphyxia. In the process of affording this one small advantage, the incision substantially increases maternal blood loss, the average depth of posterior perineal injury, the risk of anal sphincter damage and its attendant long-term morbidity (at least for midline episiotomy), the risk of improper perineal wound healing, and the amount of pain in the first several postpartum days.