Objective: Our purpose was to determine the rate of associated risk factors for shoulder dystocia from a large cohort of patients delivered within our Southern California perinatal program. Study design: A retrospective analysis was performed of patients delivered from January 1991 to June 2001. Patients with and without shoulder dystocia were identified from our computer- stored perinatal database and compared. Statistical methods used included: χ 2 test, t test, calculation of odds ratios, and Fisher exact test, as indicated. Results: Among the 267,228 vaginal births during the study period, there were 1,686 cases of shoulder dystocia (rate 0.6% ). Rates for operative vaginal delivery, diabetes, epidural use, multiparity, and postdatism were similar among cases with and without shoulder dystocia. The clinical triad of oxytocin use, labor induction, and birth weight greater than 4,500 g yielded a cumulative odds ratio of 23.2 (95% CI 17.3- 31.0) for shoulder dystocia, but its sensitivity and positive predictive value were only 12.4% and 3.4% , respectively. Conclusion: Historic obstetric risk factors for shoulder dystocia are not useful predictors for the event. Furthermore, although shoulder dystocia was observed more frequently with increasing birth weight, current limitations in estimating birth weight antenatally with accuracy preclude its practical use as a reliable predictor. Objective: Our purpose was to determine the rate of associated risk factors for shoulder dystocia from a large cohort of patients delivered within our Southern California perinatal program. Study design: A retrospective analysis was performed of patients delivered from January 1991 to June 2001. Patients with and without shoulder dystocia were identified from our computer-stored perinatal database and compared. Statistical methods used included: χ 2 test, t test, calculation of odds ratios, and Fisher exact test, as indicated. Results: Among the 267,228 vaginal births during the study for, there were 1,686 cases of shoulder dystocia (rate 0.6%). Rates for operative vaginal delivery, diabetes, epidural use, multiparity, and postdatism were similar among cases with and without shoulder dystocia. The clinical triad of oxytocin use, labor induction , and birth weight greater than 4,500 g yielded a cumulative odds ratio of 23.2 (95% CI 17.3- 31.0) for shoulder dystocia, but its sensit ivity and positive predictive value were only 12.4% and 3.4% respectively, respectively. Conclusion: Historic obstetric risk factors for the shoulder dystocia were not predictive predictors for the event. birth weight antenatally with accuracy preclude its practical use as a reliable predictor.