Horizontal profiles of F region plasma density from the Sondrestrom incoherent scatter radar facility (66.99 ¿N latitude, 50.95 ¿W longitude) are used to determine the large-scale structure and statistical distribution of ionospheric plasma during polar cap patch events. Large-scale latitudinal gradients in average electron density were observed coincident with primarily meridional flow, suggesting the plasma decayed with time constants of the order of 1 hour. Plasma density distributions for each of the five nights in the data set were characterized by peaks at low plasma densities representing the background plasma, with the presence of patches typically resulting in a tail in the high-density regime of the distribution. Observed patch sizes averaged ~400 km, with a most probable value in the 200- to 300-km range. Patch edges were found to be characterized by gradient scale lengths of ~100 km, significantly smaller than the typical 400-km scale length of background gradients. Gradients interior to patches were intermediate in magnitude, with average scale lengths of ~275 km. The general characteristics of the patches in these data, including their occurrence in latitude and local time, are consistent with an origin in a tongue of ionization. The observed distributions of patch scale sizes and density enhancement ratios verify the general features of earlier results from satellite measurements. The relatively short decay time constants inferred from this data set suggest that patches do not survive long enough to make multiple passes through the convection pattern and that their impact as a source of auroral zone blobs may be mostly limited to the nightside ionosphere. ¿ 1998 American Geophysical Union