The complexity of hospital emergency department operations limits comprehension and inhibits efforts to improve efficiency. Attempts have been made to reduce the complexity by streaming patients into similar classes of treatment or grouping them into similar cases. These have not successfully modeled the treatment of patients. This paper describes how the combination of a process philosophy with data mining resulted in the discovery of definitive "treatment pathways". These pathways comprehensively model treatment of patients. Examination of these pathways indicated that the ratio of treatment procedures remained fairly constant. It was concluded that workload in the emergency department varies only by number of presentations, not in type of procedure carried out. Some applications of this knowledge are discussed.