Managers, physicians and researchers need to study patient's path for purposes of management, quality of care and research. We present the proof of concept of the use of a flow diagram, the Sankey diagram, to visualize the trajectory of a population that experienced an event. This representation was tested with two case studies in populations from the anesthesia data warehouse of Lille University Hospital. For the 551 patients undergoing a pancreaticoduodenectomy, Sankey diagram helped us identify atypical care paths of patient being transferred too late in an intensive care unit. For 473953 patients who have had anesthesia procedure, Sankey diagram highlighted that mortality and re-operation rates increase with the number of operations. This preliminary work has been well received by end-users and allowed managers, physicians and researchers to visualize the paths of patients and to provide visualization support for research questions. This work will be followed by generalization.