Recent developments in wireless sensor networks have inspired applications which require high accuracy localization. Impulse radio ultra wide-band technology has a fine time resolution, allowing accurate determination of the time of arrival at the receiver, making it a serious contender for accurate ranging, in comparison to narrow-band technologies. In this paper, we present a UWB based 3D real-time indoor positioning system with 802.15.4a compliant wireless nodes. Results from measurement campaigns reveal that for line-of-sight (LOS) scenarios 11 cm accuracy and 2 cm precision without any postprocessing (i.e. filtering) are possible, hence demonstrating the capability of accurate UWB-based localization using trilateration, resulting in a fast and non-complex algorithm that provides highprecision positioning. The proposed system presents an initial step in developing a high precision system for localization in industrial applications.