There was a steady increase in the yearly cesarean delivery rate, from 14.0 to 24.8%, between July 1, 1978 and June 30, 1986 at Duke University Medical Center; this was associated predominantly with an increase in the rate of primary cesarean deliveries. The three most frequent major diagnoses associated with primary cesarean delivery changed significantly over the study period. Fetal compromise became the most commonly associated diagnosis (from third), dystocia second (from first), and maternal disease third (from second). The categories of fetal positional abnormalities (fourth), abnormalities of placentation (fifth), and multiple pregnancy (sixth) did not change in rank. Primary cesarean delivery patients were compared with patients who delivered vaginally using odds ratios, prevalence, and population- attributable fractions. The risk factors of nulliparity, gestational age less than 37 weeks, late decelerations, and referral had the largest impact on the primary cesarean rate. Decreases in rates related to an increased tolerance of abnormalities of labor were overshadowed by the effects of increased concerns related to fetal health.