In this study we present a comparison between the properties of the ionospheric ion streams in the Earth's magnetotail and the predictions of a two-dimensional kinetic model for the transport of ionospheric ions from the cleft topside ionosphere into the tail lobes. General agreement is apparent between average data and model with appropriate assumptions for the ionospheric source. The same general features in the topology and similar numerical values of the stream density and velocity appear in the data and in the model predictions. However, variations associated with varying magnetic activity levels do not appear to be well modelled yet. In particular the assumption that magnetospheric activity as represented by the AE index, and the model numerical values of the cross-tail electric field might be simply related to each other does not prove to be satisfactory. Model sophistication and data coverage and organization will have to be improved to study these effects in deeper detail. ¿ American Geophysical Union 1988