Creation of the Root Cause Analysis (RCA) represents a phase of clinical risk management and is the instrument chosen for reactive analysis of adverse events. It is important to consider RCA in the context of the entire clinical risk management process and to understand the interrelationships with the previous and subsequent phases, in order to identify the necessary input and the expected output of such activity. In this study the input consisted of the adverse event which occurred after a health worker had been exposed to a biological risk and the "source patient sample" could not be found. The hospital and nursing authorities analyzed the event to understand its dynamics and causes. The results, or output, obtained indicate the steps necessary to go on to the next phase, namely treatment of the risk and the need for systemic measures: improvement of communication , revision of hospital procedures for managing blood samples and modification of the laboratory computer programs.