We report on a case of massive wear because of an incompatible metal-on-metal combination. In a 62-year-old man, a cobalt-chromium (CoCr) inlay and a stainless steel head were paired by accident. Because of persistent pain, revision surgery was performed 7 months later. Histologic analysis of the surrounding tissue revealed massive metallosis. The wear volume was increased by a factor of 18 for the head and 2 for the cup compared with normal metal-on-metal articulation. The serum concentrations of chromium and cobalt were increased by a factor of 20 and 4 over levels of a healthy population, respectively. Incompatible metal-on-metal combinations should be revised immediately. In case of delayed diagnosis, no metal-on-metal articulation should be implanted because of the high volume of metal in the human body.