The effect of cesarean section on the condition at birth in cases of preterm breech presentation was studied in consecutively delivered infants in two time periods. Delivery was rarely (8%) by cesarean section in 1961 to 1974 and usually (89%) by cesarean section in 1978 to 1984. The increased cesarean rate did not reduce the incidence of severe depression, which was double that in control cases with cephalic presentations in both periods. Breech births did not have a higher mortality rate than cephalic births in either period; birth trauma and encephalopathy were similar in both periods. Cesarean section was therefore not found to reduce either the incidence of depression at birth or the mortality. However, head entrapment was responsible for the deaths of seven of 55 live-born infants delivered vaginally at 25 to 28 weeks' gestation, all weighing less than 1000 gm. Although cesarean section is at present performed least often among these extremely premature infants, it is in these cases that it may prove most beneficial.