The pervasiveness of reasoning errors in emergency care (EC) is commonly acknowledged in clinical research. Much of this work has focused on diagnostic errors; yet, in EC, providing a specific diagnosis is generally secondary to managing the patient. To gain insights into non-diagnostic, treatment-related errors, we presented EC residents with computer-based case simulations and recorded their actions and verbalized thoughts. Nearly all participants diagnosed both study cases correctly yet made a variety of patient management errors, some with serious consequences. More substantial errors could be classified as stemming from incorrect patient status and treatment inferences. These EC reasoning errors are discussed within the framework of underlying cognitive processes.