Using data from the high-altitude plasma instrument on board the DE 1 spacecraft, we have estimated the perpendicular (to the magnetic field) extent of the region of ion injection into the cusp by measuring the energy dispersion of the ion V-shaped signatures seen on energy-time spectrograms. Three different passes were chosen based on the clarity of the V-shaped ion signatures. These studies indicate that the injection region has a dimension perpendicular to the magnetic field in the range 1000 km<D<6000 km at a radial distance of ~10 RE, in good agreement with reported diameters of flux transfer events (FTEs). Similar measurement of the energy dispersion of an electron V-shaped signature observed on one pass has yielded a parallel extent of the plasma injection region in the range 100 km<D∥<350 km. Our results lead to the suggestion that the plasma within an FTE travels down the field lines as the field line convects antisunward, and may subsequently be observed in the polar cusp as a V-shaped signature. ¿ American Geophysical Union 1988