Fetal macrosomia is associated with increased risk of dystocia and birth trauma. Elective Cesarean section has been recommended for macrosomic fetus to prevent the associated complications. However, the cost/benefit ratio of such practice should be known before it can be considered appropriate.The record of 6230 women delivered consecutively at Tri-Service General Hospital were reviewed retrospectively. The occurrence rates of dystocia and birth trauma were compared between normal birthweight group (2500-3999 gm) and macrosomic group (> or = 4000 gm). The complication rates were calculated specifically among those macrosomic infants delivered vaginally.Of the 6230 singleton pregnancies, 207 had an infant weighing at least 4000 gm. One hundred and three macrosomic infants were delivered by Cesarean section. The indication for Cesarean section was dystocia in 25, estimated fetal macrosomia in 30 and other, 48. If only those pregnancies with macrosomic infant allowing an adequate trial of labor were considered, the frequency of Cesarean section for dystocia was 19.1% in the 4000-4999 gm group and 21.4% in the 4500 gm group, compared with 4.4% in the normal birthweight group. No birth trauma occurred in the macrosomic infants delivered by Cesarean section. Of those macrosomic infants delivered vaginally, the frequency of clavicle fracture was 11.8% in the 4000-4499 gm group and 18.2% in the > or = 4500 gm group, compared with 1.2% in the normal birthweight group. Two infants (18.2%) weighing greater than 4500 gm sustained brachial plexus injury.Elective Cesarean section on macrosomic infants to prevent dystocia is not recommended because most of them can be delivered vaginally. For the very macrosomic infants (> or = 4500 gm), elective Cesarean section is suggested to prevent birth trauma.