OBJECTIVE To estimate the national incidence of peripartum hysterectomy and quantify the risk associated with cesarean deliveries and other factors. METHODS A population-based, matched case-control study using the United Kingdom Obstetric Surveillance System, including 318 women in the United Kingdom who underwent peripartum hysterectomy between February 2005 and February 2006 and 614 matched control women. RESULTS The incidence of peripartum hysterectomy was 4.1 cases per 10,000 births (95% confidence interval [CI] 3.6-4.5). Maternal mortality was 0.6% (95% CI 0-1.5%). Previous cesarean delivery (odds ratio [OR] 3.52, 95% CI 2.35-5.26), maternal age over 35 years (OR 2.42, 95% CI 1.66-3.58), parity of three or greater (OR 2.30, 95% CI 1.26-4.18), previous manual placental removal (OR 12.5, 95% CI 1.17-133.0), previous myomectomy (OR 14.0, 95% CI 1.31-149.3), and twin pregnancy (OR 6.30, 95% CI 1.73-23.0) were all risk factors for peripartum hysterectomy. The risk associated with previous cesarean delivery was higher with increasing numbers of previous cesarean deliveries (OR 2.14 with one previous delivery [95% CI 1.37-3.33], 18.6 with two or more [95% CI 7.67-45.4]). Women undergoing a first cesarean delivery in the current pregnancy were also at increased risk (OR 7.13, 95% CI 3.71-13.7). CONCLUSIONS Peripartum hysterectomy is strongly associated with previous cesarean delivery, and the risk rises with increasing number of previous cesarean deliveries, maternal age over 35 years, and parity greater than 3. METHODS II.