The isotropic-nematic phase transition in a fluid of hard spherocylinders with a spherocylindrical square-well attraction is examined using Monte Carlo simulations and two theoretical approaches. The first theory is a first-order perturbation theory which incorporates the Parsons decoupling approximation for the pair distribution function. The second theory is a simple resummation of the virial coefficients in the nematic phase which maps the thermodynamics of the nematic phase to those of the isotropic phase. In general both the theoretical approaches and the simulation results show a destabilization of the nematic phase with respect to the isotropic phase as the temperature is decreased. However, close comparison between the simulation results and the theories reveals that the Parsons approach is quantitatively deficient. On the other hand, the results for the resummation procedure are in good agreement with the simulation results over the full isotropic range and for the isotropic-nematic phase transition. The comparison of the nematic phase close to the phase transition shows reasonable agreement between theory and simulation, however, the theoretical results become much poorer deep in the nematic phase. The reason for this is attributed to the crude manner in which the orientational dependence is included into the attractive contribution to the free energy.