The fabrication and behavior of an all‐carbon cathode for the growth of diamond films by dc discharge plasma chemical vapor deposition is presented. A graphite rod with a diameter of 2.5 mm was passivated in a methane dc plasma. During this process, the graphite was coated with pyrolytic carbon. Simultaneously, a thorn shaped protuberance (hereafter referred to simply as the thorn) of the same material grew from the end face of the rod towards the anode. The pyrolytic carbon prevented excessive sputtering of the cathode during diamond film synthesis in the hydrogen–methane plasma and the thorn presented a pointlike electron emitter providing a stable discharge. Using such cathodes, polycrystalline diamond films with well faceted crystallites have been grown at rates of approximately 5 &mgr;m/h. Nucleation and growth of individual, well faceted diamond crystallites even occurred on the cathode. When producing diamond films at methane concentrations above 1 vol %, a tubular form grows on the end of the cathode thorn.