Experimental and numerical investigations of the field emission of a single molybdenum Spindt emitter are presented. Experimental results show that the emission is localized at nanometric areas on the top of the tip. An effective numerical model of the tip has been developed to describe the main characteristics of the experimental beam pattern. The Lagrange constant of this model has been estimated to 15 nm V-1/2. (c) 2005 American Vacuum Society.