A sealed gas photon detector with a gas electron multiplier (GEM) cascade coupled to a semitransparent CA photocathode has been studied. High gains, reaching 10(6), and fast anode signals, of a width of 15 ns, were obtained with this GEM-photomultiplier in Ar-CH4 (95/5), in a photon counting mode. The lifetime of this first prototype detector under high photon flux and large anode currents is provided.