  Thermal corrections, including relativistic effects, for the positronium atom
are discussed. The theoretical description of thermal corrections is carried
out within the framework of relativistic quantum electrodynamics. As a result,
thermal corrections to atomic energy levels with a fine and hyperfine structure
and to the probabilities of annihilation of a positronium atom placed in a
thermal environment (blackbody radiation) are taken into account. Numerical
results are discussed throughout the paper in view of modern experiments and
theoretical searches for verification of fundamental interactions.
