The emission properties of cesiated silicon cold cathodes are described and the factors which ultimately limit the performance of such cathodes are discussed. It is tentatively concluded that the maximum available current density and brightness are limited by cesium migration and desorption, these maximum values (for emitters with 1 μm diam and with an efficiency of 1.5%) beingjvac,max≂1500 A/cm2andBmax≂9×106A/cm2sr (atV=10 kV). The long term stability of the emission is surprisingly good, in spite of adsorption of oxidizing gases from the vacuum. This indicates that there is a desorption of such gases too, probably due to the outgoing electrons at high current densities.