This master's thesis describes how to guide a robotic arm ˝Universal Robot (UR5)˝ by using the medical OTS (Optical Tracking System) Polaris Vicra, in order to reduce Positioning Errors. The introductory chapter, which is about already existing robotic systems in medicine, is followed by chapters on the operating principle of optical system and a short description of the robotic arm with its related kinematic model. There are also subsections that describe mathematical terminology and mathematical structures used by the OTS and the UR5. The calibration board was used as etalon for measurements. At the beginning of the practical part of this master's thesis, the calibration board was measured on the optical coordinate measuring machine, so that the distances between holes can be determined. The acquired distances were used as referent values. Later, all other measurement results were compared to the results obtained by the CMM. Next step was to manually measure the calibration board with the optical system in order to calculate OTS measurement errors. The errors in measurement were calculated for: • the position and orientation of only one marker; • OTS returns the data of the marker probe in the second marker's coordinate system. Marker probe was attached to the robot's end effector. By manually guiding the robot, the tip of the marker probe was centred in each hole on the calibration board in the same orientation and data was collected from the robot and the Polaris for each hole. The acquired data from the robot and from the Polaris were compared to the data from the CMM. Within this master's thesis, a controlling program has been made that provides a relative guidance of the robotic arm tool by using the data measured by the OTS. The Program is written in the C++ programming language. The software support provides all functionality specified by a given task. Comprehensive description of the entire software support, including the communication protocol between the robot and the PC, the mathematical algorithm, the exchange of information and information flow is provided in the fifth chapter. Excel tables and used programming codes are provided in the attachment at the end of this master's thesis.