Two‐dimensional magnetohydrodynamic numerical calculations have been performed to study the fuel behavior of a preconditioned relativistic electron beam target in which, experimentally, a portion of the beam current prepulse entered the target to provide fuel preheat and magneto‐thermoinsulation. The magnetohydrodynamic plasma model used includes radiation, thermal conduction, ionization, and resistive diffusion. The magnetohydrodynamic partial differential equations are solved by a computer code employing implicit finite‐difference methods. The fuel is shown to develop counter‐streaming vortices during the implosion phase. The computed neutron yield is in reasonable agreement with the experimental value, suggesting the origin of the neutrons to be thermonuclear. The effect of both magneto‐thermoinsulation and preheat is examined.