The electronic structure of MnSi is calculated using the LMTO method. We show total energy results and densities of states for different lattice constants of both paramagnetic and spin-polarized calculations. Magnetic moments and exchange splittings are given as a function of pressure. The structural stability of the magnetic phase is discussed in terms of Stoner's criterion and from total energy calculations. The ground state is found to be magnetic for all lattice constants ranging from 8.30 to 9.10 a.u.