Objective: To estimate whether immediate or delayed pushing in the second stage of labor optimizes spontaneous vaginal delivery and other perinatal outcomes. Data Sources: We searched electronic databases MEDLINE and CINHAL through August 2011 without restrictions. The search terms used were MeSH headings, text words, and word variations of the words or phrases labor, laboring down, passive descent, passive second stage, physiologic second stage, spontaneous pushing, pushing, or bearing down. Methods Of Study Selection: We searched for randomized controlled trials comparing immediate with delayed pushing in the second stage of labor. The primary outcome was spontaneous vaginal delivery. Secondary outcomes were instrumental delivery, cesarean delivery, duration of the second stage, duration of active pushing, and other maternal and neonatal outcomes. Heterogeneity was assessed using the Q test and I. Pooled relative risks (RRs) and weighted mean differences were calculated using random-effects models. TABULATION, INTEGRATION, AND Results: Twelve randomized controlled trials (1,584 immediate and 1,531 delayed pushing) met inclusion criteria. Overall, delayed pushing was associated with an increased rate of spontaneous vaginal delivery compared with immediate pushing (61.5% compared with 56.9%, pooled RR 1.09, 95% confidence interval [CI] 1.03-1.15). This increase was smaller and not statistically significant among high-quality studies (59.0% compared with 54.9%, pooled RR 1.07, 95% CI 0.98-1.26) but larger and statistically significant in lower-quality studies (81.0% compared with 71.0%%, pooled RR 1.13, 95% CI 1.02-1.24). Operative vaginal delivery rates were high in most studies and not significantly different between the two groups (33.7% compared with 37.4%, pooled RR 0.89, 95% CI 0.76-1.06). Delayed pushing was associated with prolongation of the second stage (weighted mean difference 56.92 minutes, 95% CI 42.19-71.64) and shortened duration of active pushing (weighted mean difference-21.98 minutes, 95% CI-31.29 to-12.68). Conclusion: Studies to date suggest there are few clinical differences in outcomes with immediate compared with delayed pushing in the second stage of labor, especially when high-quality studies are pooled. Effects on maternal and neonatal outcomes remain uncertain.