[Monitoring of clinical trials and interim analysis. 1. Monitoring committee].

In order to fulfil the ethical principles linked to the protection of patients randomized in a controlled clinical trial, monitoring procedures need to be set up. In this context, a committee of experts, called the data monitoring committee is in charge of reviewing regularly unblinded data to assess the quality and the relevance of the trial, to evaluate the evidence of an emerging treatment difference and to control the rate of occurrence of serious adverse events. After each meeting, the monitoring committee reports to the steering committee its recommendation to continue or to stop the trial prematurely. Protocol modifications might be proposed as well. Illustrated with several examples, this article reviews different situations a monitoring committee might have to tackle with.