In this paper we propose a 3-D imaging method combining the concepts of monopulse imaging and wideband ISAR imaging. The field backscattered from a rotating object is received by two vertically-displaced antennas. From the fields received by the two antennas we can obtain a 3-D image which provides information about scattering strength and the 3-D position parameters (down range, cross range, and height) of the object's scattering centers. This method does not unduly increase the complexity of the data acquisition or computing load in the image reconstruction. Numerical and experimental results show the effectiveness of the proposed method. However, when multiple scattering centers are collocated at the same projective coordinate with different height, the proposed method fails to separate the scatterers.