A new algorithm for the reconstruction of three-dimensional images of ionospheric electron density using volumetric a priori information is presented in this paper. This method relies upon the total electron content (TEC) data measured by an ionospheric tomography system to derive necessary distribution-related information from a priori ionospheric images for projection domain and image domain volumetric correction processes. It involves extraction of shape information from a priori ionospheric images on an extremely localized basis to simultaneously satisfy measured TEC data and the need for coherent, convergent reconstruction guidance, necessary for the limited angle tomography system. The algorithm uses three-dimensional polar geometry for computerized ionospheric tomography (CIT) which permits direct use of slant TEC data without the interpolations that are necessary for conventional two-dimensional imaging of the ionosphere. Reconstructions based on data recorded in two recent CIT campaigns are also presented. ¿ 1998 American Geophysical Union