We present an ultrasound vibro-elastography system designed to acquire viscoelastic properties of the prostate and peri-prostatic tissue. An excitation stage imparts low-frequency (<20 Hz), limited amplitude (<± 2mm), broadband vibratory motion to an endorectal transducer, along a radial/transversal direction. The induced tissue motion is estimated from ultrasound radio-frequency data and is used to estimate the mechanical frequency response of tissue to the excitation at different spatial locations. This can be used to determine the spatial distribution of various mechanical parameters of tissue, such as stiffness and viscosity. Phantom and in-vivo images are presented. The results obtained demonstrate high phantom and tissue linearity and high signal-to-noise ratio.