Percutaneous intervention is essential in numerous medical diagnostic and therapeutic procedures. In these procedures, accurate insertion of the surgical needle is very important. But precise interstitial intervention is quite challenging. Robot-assisted needle intervention can significantly improve accuracy and consistency of various medical procedures. To design and control any robotic system, the design and control engineers must know the forces that will be encountered by the system and the motion trajectories that the needling mechanism will have to follow. Several researchers have reported needle insertion forces encountered while steering through soft tissue and soft material phantoms, but hardly any in-vivo force measurement data is available in the literature. In this paper, we present needle insertion forces and motion trajectories measured during actual brachytherapy needle insertion while implanting radioactive seeds in the prostate glands of twenty five patients.