To elicit components of task complexity in emergency medical care, a study was conducted to contrast one medical procedure with two levels of task urgency in trauma patient resuscitation. Videotapes of actual resuscitation were reviewed to extract task characteristics of the procedure. Two levels of urgency were compared in the following areas: patient status, technical difficulty of tasks, the amount of available patient monitoring information, and the pace of work. Four components of task complexity in emergency medical care were identified: multiple and concurrent task, uncertainty, changing plans, and compressed work procedures and high workload. These components of task complexity pose challenges to team functions and can lead to problems in team coordination, such as conflicts in goals, tasks, and access to the patient. Training to increase explicit communications and improvements in the design of work procedures are necessary in order to meet the challenges of task complexity.