We describe a new procedure for three-dimensional (3D) region-of-interest (ROI) reconstruction from transverselytruncated cone-beam projections acquired with a circular source trajectory. This method is an extension to 3D of the virtual fan-beam (VFB) method. It is based on a VFB formula that performs the backprojection in the acquisition geometry. Our simulation results show that the ROI reconstruction of the 3D Shepp-Logan phantom is very similar to the one obtained by the Feldkamp, Davis, Kress (FDK) algorithm without truncation. However the reconstruction of the Forbild head phantom shows artefacts which are absent from the FDK truncation-free reconstruction.