Retained surgical items (RSIs) are rare but serious events associated with significant morbidity and costs. We assessed the effectiveness of radiofrequency (RF) detection technology and Team Strategies and Tools to Enhance Performance and Patient Safety (TeamSTEPPS) in reducing the incidence of RSIs. All RSIs reported to the New York Patient Occurrence Reporting and Tracking System at five large urban teaching hospitals from 2007 to 2017 were analyzed. In 2012, TeamSTEPPS training was provided to all perioperative staff at each site, and use of RF detection became required in all procedures. The incidence of events before and after the interventions were compared using odds ratios. A total of 997,237 operative procedures were analyzed. After the interventions, the incidence of RSIs decreased from 11.66 to 5.80 events per 100,000 operations (odds ratio [OR] [95% CI] = 0.50 [0.32 to 0.78]). The frequency of RSIs involving RF-detectable items decreased from 5.21 to 1.35 events per 100,000 operations (OR [95% CI] = 0.26 [0.11 to 0.60]). The difference in RSIs involving non-RF-detectable surgical items was not statistically significant. The incidence of RSIs was significantly lower during the time period after implementing RF detection technology and after TeamSTEPPS training, primarily driven by a decrease in retained RF-detectable items. RF detection technology may be worth pursuing for hospitals looking to decrease RSI frequency. The benefit of TeamSTEPPS training alone may not result in a reduction of RSIs.