Effective teamwork during clinical emergencies is required for optimal outcomes for patients. Failure of a medical team in a critical situation can result in permanent patient harm and medical litigation. It is logical, therefore, that proper training in teamwork during emergencies should be a priority in reducing preventable patient harm. However, the specific aspects of teamwork that lead to effective clinical care have not been clearly identified. This cross-sectional, secondary analysis of video recordings of teams performing in a large, randomized, controlled simulation trial in southwest England explored team performance and behaviors (leadership, communication, and task allocation) that affected management of an obstetric emergency. Recruitment for the Simulation & Fire-drill Evaluation study occurred in 2004 to 2005, with 24 staff members randomly selected from each of 6 secondary and tertiary maternity units and allocated to teams of 1 senior and 1 junior doctor and 2 senior and 2 junior midwives. They participated in an obstetric emergency simulation scenario that was video recorded. A list of behaviors, derived from a 2009 literature review of teamwork studies, was used by a steering group of language/communication, psychology, and midwifery researchers; obstetricians; and a statistician to develop a practical assessment tool for teamwork. The assessment grid developed by the steering group was used by 2 independent assessors, a clinician and a language communication specialist, to evaluate specific teamwork behaviors seen in the videos. For this report, a cross-section of 114 healthcare professionals in 19 teams were analyzed from video recordings of the teams managing a simulated case of eclampsia. The “patient” simulated a 1-minute seizure, starting 60 seconds after the handover of the patient to the team, and the drill was concluded after 10 minutes. The main outcome measure was the relationship between teamwork behaviors and the time to magnesium sulfate (MgSO4) administration for seizure control and secondary prevention. A validated clinical efficiency score was used to evaluate the teamwork behaviors. The most efficient teams were more likely to recognize and state the emergency using unambiguous terminology earlier than less-efficient teams. (Two teams never stated the nature of the emergency). They also used closedloop communication (task clearly and loudly delegated, accepted, executed, and completion acknowledged). Twelve teams administered MgSO4 within the allotted 10 minutes period with a median handover-to-administration time of 415 seconds; the least efficient team did not even discuss the need for MgSO4 during the study period. The most effective teams had significantly fewer exits from the labor room compared with the other teams (median exits 3 vs. 6). A correlation was suggested between the clinical efficiency score and whether an SBAR style of communication (situation, background, assessment, and recommendation) was used during handover to the senior doctor, with the most efficient teams more likely to use SBAR. For all groups, there was a lack of explicit declaration of leadership throughout and no clear transfer of command at any point, although the senior doctor seemed to be the leader in most drills. (In 1 team, the senior physician was never called to help). Very few instances of supportive behavior or language were observed in any of the simulations. The authors concluded that there is a relationship between clinical performance and defined teamwork behaviors in a healthcare emergency. In the past, teamwork training has been based largely on opinion, not scientific evidence; however, the results of this study suggested that it is possible to analyze team behaviors using a structured and validated assessment tool. They recommended future studies be performed to determine whether these findings are relevant to real-time emergencies and generalizable to other specialties.