Electron number density (Ne) profiles determined remotely by ISIS 1 and 2 topside sounder measurements were compared with in situ ion and electron density measurements by the Dynamics Explorer 2 (DE 2) Langmuir probe during four high-latitude ISIS/DE magnetic field-aligned conjunctions. In all cases, the universal time separations between the two data sets were small (less than 12 min). The horizontal separations away from conjunction were up to several thousand kilometers. The Ne comparisons near the conjunction times represents the first cross-calibration of in situ probe and remote topside sounding Ne measurements. The ISIS-derived Ne values, even at the greatest distance from the sounder (near the F peak), agreed with the DE 2 Langmuir probe measurements to within about 30% over a density range of more than 2 decades on three of the comparisons. The fourth comparison, which only had data on one side of the conjunction in a region with strong Ne irregularities, showed a difference of about 60%. Away from conjunction the Ne comparisons were made by displaying Ne along the orbital tracks on invariant latitude (&Lgr;)/magnetic local time (MLT) polar plots, or by displaying Ne versus time where the two data sets are mapped to one another either along arcs of constant &Lgr; or along radii of constant MLT. These plots display density structure simultaneously at distinct locations in the convection controlled polar ionosphere. During one of the conjunctions a comparison was made between the DE 2 electron temperature and the temperature derived from the ISIS sounder scale height. This comparison revealed a region with Te>Ti and a Te enhancement colocated with spread F (observed on ISIS), but not correlated with weak particle precipitation.