Highlights: ? Task analysis of an emergency medical service. ? Emergency personnel participated in the icon design for the medical information system. ? Understandability of the developed icons were tested by a second group of physicians and nurses. ? Final user interface was decided and installed after assessing two prototypes.Abstract: A usable medical information system should allow for reliable and accurate interaction between users and the system in emergencies. A participatory design approach was used to develop a medical information system in two Turkish hospitals. The process consisted of task and user analysis, an icon design survey, initial icon design, final icon design and evaluation, and installation of the iconic medical information system with the icons. We observed ….