During the daily treatment of patients large quantities of data are recorded in electronic health records (EHRs). Compared to data in paper records, these EHR data are easily available for reuse in research and quality improvement. However, the opportunities for reuse depend on the quality of the data. In this study we analyze the completeness with which main treatment activities are recorded on emergency department (ED) whiteboards and whether completeness varies with the severity of the patients’ condition. Data from 381231 ED visits show that after the whiteboard had been in successful use for several years the clinicians recorded four of the five main treatment activities with a completeness of less than 50%. Completeness tended to increase with three indicators of the severity of the patient’s condition: triage level, length of stay, and patient age. We conclude that the low completeness of the activity data probably prevents most types of reuse.