In the last years technological development have led to an increase in the reliability and safety of the medical devices. However it is not possible to analyze the reliability of such systems without considering the "human factor" and the man's role in the dynamics of accidents. Assessing the probability of occurrence of the error by the user is not simple, in fact the variables are many and always different depending on the context. Starting from an overview of the literature focused especially on Healthcare field, this study proposes a procedure to evaluate the risk linked to the human factor in the use of medical devices. Considering life cycle of the device, level of cognitive engagement of tasks, environmental conditions, stress, sense of responsibility, level of training and experience, this semiquantitative procedure gives information about level of risk associated to the human error in the usage of medical devices in terms of "risk indexes". In addition, it would be useful to compare more devices to each others, to reduce risk if it is applied in the design phase of the device, to facilitate users making devices more user-friendly, to improve performances and efficiency of medical devices. The procedure is applied to evaluate and compare the risk linked to the human error in the use of two in vitro diagnostic medical devices (IVD).