  In this work we analyze the Casimir energy and force for a {\it thick} piston
configuration. This study is performed by utilizing the spectral zeta function
regularization method. The results we obtain for the Casimir energy and force
depend explicitly on the parameters that describe the general self-adjoint
boundary conditions imposed. Numerical results for the Casimir force are
provided for specific types of boundary conditions and are also compared to the
corresponding force on an infinitely thin piston.
