Purpose: a comanipulator for assisting endorectal prostate biopsies is evaluated through a first-in man clinical trial. This lightweight system, based on conventional robotic components, possesses 6 degrees of freedom. It uses 3 electric motors and 3 brakes. It features a free mode, where its low friction and inertia allow for natural manipulation of the probe and a locked mode, exhibiting both a very low stiffness and a high steady state precision. Methods: Clinical trials focusing on the free mode and the locked mode of the robot are presented. The objective is to evaluate the practical usability and performance of the robot during clinical procedures. A research protocol for a prospective randomized clinical trial has been designed. Its specific goal is to compare the accuracy of biopsies performed with and without the assistance of the comanipulator. Results:The accuracy is compared between biopsies performed with and without the assistance of the comanipulator, across the 10 first patients included in the trial. Results show a statistically significant increase of the precision.. This work is partially funded french state funds managed by the ANR within the Investissements d'Avenir programme (Labex CAMI) under reference ANR-11-LABX-0004. 2 Marie-Aude Vitrani et al.