Reducing the rate of cesarean sections among women considered at low risk for delivery by that method is a goal of Healthy People 2030. Prior research suggests that perinatal mood and anxiety disorders increase the risk for cesarean section, but data are limited. This cross-sectional study of commercially insured women examined the relationship between perinatal depression and anxiety disorders and primary (first-time) cesarean section rates, using administrative claims data for US in-hospital deliveries from the period 2008-17. Of the 360,225 delivery hospitalizations among 317,802 unique women, 24.0 percent included a delivery by primary cesarean section, and 3.1 percent carried a diagnosis of depression, anxiety, or both made during the index pregnancy. Using an adjusted generalized estimating equation, we found that the predicted probability of primary cesarean section was 3.5 percentage points higher, on average, among women with these disorders compared with those without them. Our findings confirm the importance of pursuing research to identify mechanisms by which perinatal depression and anxiety disorders increase the risk for primary caesarean section among women otherwise considered at low risk for delivery by that method, as well as effective interventions.