This article presents positioning results of a stereotactic robotic assistant for percutaneous needle insertions in the abdomen. The robotic system, called the CT-Bot, is succinctly described. This mechanically safe device is compatible with medical requirements and offers a novel approach robotic needle insertion with computed tomography guidance. Our system does self-registration using only visual information from a fiducial marker. The theoretical developments explain how the pose reconstruction is done using only four fiducial points and how the automatic registration algorithm is achieved. The results concern the automatic positioning of the tip of a needle with respect to a reference point selected in a CT-image. The accuracy of the positioning result show how interesting this system is for clinical use.