A case simulating extraordinarily extensive chronic vegetating pyoderma revealed itself in its course to be pyoderma gangrenosum. The bacterial flora varied due to a secondary colonization; there was no response to antibiotics but there was to corticosteroid, azathioprine and clofazimine therapy. IgA-paraproteinemia was found. Pyoderma gangrenosum has historically been considered to be a chronic ulcerous pyoderma and is not a disease of bacterial origin. Reviewing the literature available since the turn of this century, chronic vegetating pyoderma is compared with the latter from the viewpoint of clinical features, histopathology, immunology, course and treatment. There are so many convincing parallels between the two conditions that we would like to propose that we stop regarding them as distinct entities and instead view them as parts of a spectrum of the same immunopathological process.