In this paper, a full two-dimensional (2-D) quantum mechanical (QM) device simulator for deep submicron MOSFETs is presented. The model couples a 2-D Schrodinger-Poisson solver with a semiclassical transport model. The validity of the proposed model is first tested against a QM model for transport, developed as a benchmark. Then, QM effects on nanoscale MOSFETs performance are quantitatively addressed and discussed. It is shown that QM effects strongly influence the device performance, namely subthreshold slope drain-induced barrier lowering and short-channel effects. These results show that full QM simulations will become a mandatory issue for nanoscale MOSFETs modeling and design.