Effective team communication is essential to ensure patient safety, yet little is known regarding team behavior in clinical settings during critical events. This study examines differences in key team behaviors between physicians and nurses during simulated critical events. Perinatal staff participated in 11 in-situ simulation trials over a six-month period involving 8 MDs, 17 RNs, and 20 other staff. Videotapes of simulations were evaluated and scored to assess five categories of communication behaviors over different stages of OB critical events scenarios. Results indicate that physician and nurse professionals performed differently on key behavioral markers during critical events, and such performance is associated with different phases of team formation and reformation. Implications for patient safety are discussed.