OBJECTIVE: This study was undertaken to assess the utility of the nulliparous term singleton vertex cesarean birth (NTSV CB) measure as a quality improvement tool for use at the hospital level. STUDY DESIGN: We prospectively collected data on all NTSV births in Sutter Health's 20 birthing units over a 3-year period, 2001 through 2003, totaling 41,416 births. Hospital rates of NTSV CB, obstetric practices, and infant outcomes were calculated and compared by using weighted logistic analyses. In addition, we examined the effect of maternal age on the NTSV CB measure by using direct standardization with US norms for nulliparous women. RESULTS: There was large variation noted in the NTSV CB rate among the 20 hospitals, with unadjusted rates ranging from 10.5% to 30.2%. Strong correlations were found between CB rates and labor induction rates (r = 0.57, P < .0001) and with early labor admission rates (r = 0.62, P < .0001). The strongest correlation was found between NTSV CB rates and a combined measure of induction and early labor admission (r = 0.73, P < .0001). Rates of term 5-minute Apgar score below 7 were not correlated with the NTSV CB rate. Hospital nulliparous maternal age distribution varied markedly and direct standardization led to significant changes in the NTSV CB rate. CONCLUSION: NTSV CB rate is strongly influenced by elective obstetric practices. The addition of an easily performed maternal age adjustment makes it the most promising CB quality measure for use at the hospital level.