This paper discusses the adoption of multi-area reliability concepts in the evaluation of Brazilian power system capacity to supply the peak load. In the assessment of the interconnected hydrothermal power systems reliability it is adopted a computational model that takes into account uncertainties on the streamflows into the hydro plants reservoirs, random forced outages of generating units and interconnections among subsystems, system load curve and programmed outage of generating units. The model allows both single area and multi-area analysis. The calculated reliability indices can help the identification of possible power system deficiencies to supply the forecasted maximum peak load as well as the computation of power marginal costs in libelarized electricity markets. In addition, it is discussed an approach to estimate the maximum peak load that a hydrothermal generation system can supply considering a multi-area reliability criterion based on adequacy analysis. The obtained results encourage the continuity of studies seeking the establishment of such criterion for hydrothermal interconnected systems.