  We compute the scattering amplitude in Wilson Chiral Perturbation Theory for
two flavors. The lattice spacing effects due to the explicit chiral symmetry
breaking are kept through O(a^2), and we consider the regime where the quark
mass m is of order a^2 Lambda_^3. Analytic expressions for the scattering
lengths in different isospin channels are given. As a result of the O(a^2)
terms the scattering lengths do not vanish in the chiral limit. Moreover,
additional chiral logarithms proportional to a^2 ln M_pi^2 are present in the
one-loop results. These contributions can obscure the continuum chiral
logarithms and the determination of low-energy constants from numerical lattice
simulations.
