  We examine a hot pion gas by including medium modifications of the two-body
scattering amplitude as well as mean-field effects selfconsistently. In
contrast to earlier calculations, the in-medium T-matrix is rather close to the
free one while the mean-field potential agrees well with lowest-order
estimates. We also discuss the validity of the quasiparticle approximation. It
is found that it is reliable for temperatures up to $\sim 150$ MeV. Above this
temperature off-shell effects in the pion selfenergy become important,
especially if the pions are strongly out of chemical equilibrium.
