In this paper the steady-state proton distribution in the Earth's magnetotail is derived both in configuration and velocity space, taking into account the proton's energization in the dawn-dusk electric field and its motion due to deterministic chaos. This stochastic motion effectively leads to pitch angle scattering and a redistribution of protons between the central plasma sheet and its boundary, the plasma sheet boundary layer. Knowledge of these effects allows us to explain the previously observed features of the ion distribution and to predict others for future experimental work. ¿ American Geophysical Union 1990