  We study theoretically the disorder-induced smearing of the density of states
in a two-dimensional electron system taking into account a spin-orbit term in
the Hamiltonian of a free electron. We show that the characteristic energy
scale for the smearing increases with increasing the spin-orbit coupling. We
also demonstrate that in the limit of a strong spin-orbit coupling the diagrams
with self-intersections give a parametrically small contribution to the
self-energy. As a result, the coherent potential approximation becomes
asymptotically exact in this limit. The tail of the density of states has the
energy scale which is much smaller than the magnitude of the smearing. We find
the shape of the tail using the instanton approach.
