  Starting with the two-loop effective potential of the MSSM, and assuming a
supersymmetric scale well above $M_Z$, we derive a simple analytical
approximation for the lightest CP-even Higgs boson mass including resummation
of higher order logarithmic terms via RG-improvement and finite non-logarithmic
terms up to ${\cal O}(\alpha_s\alpha_t)$. This formula describes the most
relevant radiative corrections to the MSSM Higgs boson mass, in particular,
those associated with non-zero top-squark mixing.
