Obstetrical brachial plexus palsies (OBPP) have been historically attributed to the impaction of the fetal shoulder behind the symphysis pubis and to excessive lateral traction of the fetal head during maneuvers to deliver the fetal shoulders in shoulder dystocia. Shoulder dystocia is indeed a major risk factor as it increases the risk for OBPP 100-fold. The incidence of OBPP following shoulder dystocia varies widely from 4% to 40%. However, a significant proportion of OBPPs are secondary to in utero injury. The propulsive forces of labor, intrauterine maladaptation, and compression of the posterior shoulder against the sacral promontory as well as uterine anomalies are possible intrauterine causes of OBPP. Many risk factors for OBPP may be unpredictable. Early identification of risk factors for shoulder dystocia, as well as appropriate management when it occurs, may improve our ability to prevent the occurrence of OBPP in those cases that are caused by shoulder dystocia.