  This work is concerned with the phase diagram of Wilson fermions in the mass
and coupling constant plane for two-flavor (unquenched) QCD. We show that as
the continuum limit is approached, one can study the lattice theory using the
continuum chiral Lagrangian, supplemented by additional terms proportional to
powers of the lattice spacing. We find two possible phase structures at
non-zero lattice spacing: (1) There is an Aoki phase of spontaneously broken
flavor and parity, with two massless Goldstone-pions, and a width $\Delta m_0
\sim a^3$; (2) There is no spontaneous symmetry breaking, and all three pions
have equal mass of order $a$. Present numerical simulations suggest that the
former option is realized.
