We analyzed the records of 454,668 births in Ontario in the years 1979 to 1982 and found that the cesarean birth rate increased from 16.5 per hundred deliveries in 1979 to 18.7 in 1982. Cesarean births were classified according to four indications: previous cesarean birth, breech presentation, dystocia, and fetal distress. The increase in the cesarean rate for each indication from 1979 to 1982 was calculated and expressed as a percentage of the total rate increase. Previous cesarean births accounted for 68 per cent of the increase, breech presentation for 14 per cent, dystocia for 4 per cent, and fetal distress for 14 per cent. The impact of previous cesarean births was indicated by an increase in the number of women presenting with this indication--from 5.8 to 7.8 per cent of all deliveries. Although the incidence of breech presentation remained stable, the cesarean birth rate increased from 54.8 to 65 per cent for this indication. There were no marked changes in either the incidence of or cesarean rates for dystocia. The incidence of fetal distress doubled (2.4 to 4.7 per cent of deliveries), but the rate of cesarean births in these cases fell from 50.5 to 32.7 per cent. These findings suggest that physicians may have begun to respond to rising professional and public concern over the increasing cesarean birth rate, but major advances in controlling this rate can be achieved only by addressing the question of vaginal deliveries for some patients who have previously had cesarean section.