In most hospitals there are some patients who receive surgery later than required. As their health condition can potentially quickly worsen, they are exposed to a health risk. In order to improve the current situation, the lateness of patients has to be, firstly, quantified and, secondly, the responsible mechanism has to be understood, namely the patient scheduling process. We analyzed the percentage of patients being served late in Belgium’s largest hospital, the UZ Leuven. At the hospital, an elective patient is associated with one of five due time intervals within which the patient has to be served. We analyzed the lateness of patients across disciplines using all data from 2012 and 22 ORs. We tried to understand many of the different aspects related to the scheduling process, which knowledge we then included into a simulation model. We investigated from the data: patient arrival patterns, the relation between estimated and realized surgery durations, rescheduling mechanisms and the allocation patterns of emergencies. We also used the model to investigate the effects of switching from the current scheduling practice of assigning surgeries directly to slots (OR and day) to a two-step procedure, where patients are scheduled to a surgery week first and only in a second step to slots. Our results suggest that in case of the two-step procedure it is very important to allow patients with shorter due times to break into the already fixed weekly schedule. Additionally, it is important that in the second step of the scheduling procedure, in the within week scheduling, the due time is considered. We conclude that improving patient scheduling can help to decrease the amount of patients served too late. As a next step, we try to develop a sound scheduling schema, which allows to further decrease the number of patients served to late.