The development of a far-infrared imaging system based on ultrafast THz time-domain spectroscopy has opened a new field of applications of femtosecond technology. This new 'T-ray' imaging technique allows to look through or inside a variety of materials and to obtain chemical image contrast based on spectroscopic information. Using the flight-of-time information present in THz pulses reflected from compound samples we demonstrate the principle of tomographic T-Ray imaging. THz pulses are reflected from refractive index discontinuities inside an object, and the time delays of these pulses are used to determine the positions of the discontinuities along the propagation direction. This allows a 3-dimensional tomographic reconstruction of the sample's refractive index profile.