As part of the MITHRAS program, the Chatanika and Millstone Hill incoherent-scatter radars made coordinated observations of the polar ionosphere on June 27 and 28, 1981. We compare these data with predictions made by a high-latitude ionospheric model. Qualitatively, the same features are evident in both the model and the radar data: fairly constant densities on the dayside with a mid-latitude trough forming poleward of 65 degrees around 1900 MLT (magnetic local time). This trough is seen to extend equatorward with increasing MLT, such that the minimum densities occurring in the trough appear just after midnight around 60 degrees dipole latitude. These features are primarily understood in terms of different regions of convection, further influenced by photoionization and vertical transport. The only areas of major disagreement between the measurements and model are noted in the auroral oval and at a portion of the times during which substorms occurred. Quantitatively, equally good agreement is obtained between the model predictions and the radar data. The densities predicted by the model are usually within 25% of those measured by the radars, although appreciable differences occur in some regions of the ionsophere at certain times.