To compare the outcomes and costs associated with primary cesarean births with no labor (planned cesareans) to vaginal and cesarean births with labor (planned vaginal). Analysis was based on a Massachusetts data system linking 470,857 birth certificates, fetal death records, and birth-related hospital discharge records from 1998 and 2003. We examined a subset of 244,088 mothers with no prior cesarean and no documented prenatal risk. We then divided mothers into two groups: those with no labor and a primary cesarean (planned primary cesarean deliveries-3,334 women) and those with labor and either a vaginal birth or a cesarean delivery (planned vaginal-240,754 women). We compared maternal rehospitalization rates and analyzed costs and length of stay. Rehospitalizations in the first 30 days after giving birth were more likely in planned cesarean (19.2 in 1,000) when compared with planned vaginal births (7.5 in 1,000). After controlling for age, parity, and race or ethnicity, mothers with a planned primary cesarean were 2.3 (95% confidence interval [CI] 1.74-2.9) times more likely to require a rehospitalization in the first 30 days postpartum. The leading causes of rehospitalization after a planned cesarean were wound complications (6.6 in 1,000) (P<.001) and infection (3.3 in 1,000). The average initial hospital cost of a planned primary cesarean of US dollars 4,372 (95% C.I. US dollars 4,293-4,451) was 76% higher than the average for planned vaginal births of US dollars 2,487 (95% C.I. US dollars 2,481-2,493), and length of stay was 77% longer (4.3 days to 2.4 days). Clinicians should be aware of the increased risk for maternal rehospitalization after cesarean deliveries to low-risk mothers when counseling women about their choices. II.