  The Bose-Einstein correlations of two identically charged pions are derived
when these particles, the most abundantly produced in relativistic heavy ion
collisions, are confined in finite volumes. Boundary effects on single pion
spectrum are also studied. Numerical results emphasize that conventional
formulation usually adopted to describe two-pion interferometry should not be
used when the source size is small, since this is the most sensitive case to
boundary effects. Specific examples are considered for better illustration.
