  In the framework of relativistic SU(2)_f baryon chiral perturbation theory we
calculate the volume dependence of the nucleon mass up to and including O(p^4).
Since the parameters in the resulting finite size formulae are fixed from the
pion mass dependence of the large volume nucleon masses and from phenomenology,
we obtain a parameter-free prediction of the finite size effects. We present
mass data from the recent N_f=2 simulations of the UKQCD and QCDSF
collaborations and compare these data as well as published mass values from the
dynamical simulations of the CP-PACS and JLQCD collaborations with the
theoretical expectations. Remarkable agreement between the lattice data and the
predictions of chiral perturbation theory in a finite volume is found.
