To determine the main risk factors involved in neonatal clavicular fracture, the most common injury to the neonate. Two hundred fifteen cases of clavicular fracture of 65,091 vaginal deliveries (0.4%) occurring between January 1983 and December 1988 were pair-matched with controls based on mode and date of delivery, race, and maternal age. Incidences, odds ratios, and stratified analysis were used to identify and control for confounding between risk factors. Shoulder dystocia, increasing birth weight, and increasing gestational age were identified as risk factors. Within the range of normal birth weights, there is a biologic gradient of increasing risk for clavicular fracture. Although shoulder dystocia is the strongest risk factor identified, the magnitude of its point estimate is probably affected to a large extent by differential ascertainment. The use of forceps, prolonged second stage of labor, and nulliparity status were not significantly associated with neonatal clavicular fracture. Neonatal clavicular fracture occurs commonly in an obstetric population. Obstetric clavicular fracture is an unpredictable, unavoidable complication of normal birth.