Introduction : Owing to t he critical importance of emergency department activities in saving lives, information systems of this department should be free of fault to prevent the incidence of errors. Usability evaluation methods are used to assess this quality measure. Heuristic evaluation is one of the methods which identifies usability problems with minimum amount of time, cost and resources. The objective of this research was to evaluate the usability of emergency department admission subsystem of health information systems in Mashhad University of Medical Sciences .

  Methods: Using Nielsen’s 10 usability principles, three trained evaluators, independent of each other, evaluated the corresponding subsystem and determined the severity of identified problems. All the problems, identified by independent evaluators, were collected in a single list and the mean severity of each problem was calculated.

  Results: A total of 163 usability problems were identified. The lowest mismatch with usability principles was related to “error prevention” (3 %) and the highest was related to “consistency and standards” (27 %). The average severity of problems varied from 2.3 (minor problem) concerning “system's visibility” to 2.9 (major problem) concerning “help users recognize, diagnose, and recover from errors”.

  Conclusion: Heuristic Evaluation can be used to identify a high number of usability problems related to health information applications in health care systems. If remain unsolved, these problems may waste users’ and patients’ time, increase errors, reduce data quality, and in general, threaten patient’s safety.