A male with pyoderma gangrenosum is reported. The clinical and histological features were typical. The initial lesions resolved with characteristic cribriform scars. A few days after the complete recovery, he developed several necrotizing focal lesions localized to the scarred areas. A further histological examination revealed a granulation tissue rich in neutrophils and signs of necrotizing vasculitis. We found a high titer of circulating perinuclear antineutrophil antibodies (p-ANCA), which are a serological marker for various systemic diseases. An immunological circulating factor has been repeatedly suggested to be the "primum movens" of pyoderma gangrenosum. We discuss the unusual clinical presentation interpreted as a Koebner phenomenon and the possible role of immune factors in enhancing circulating-endothelial cell interactions in relation to the pathogenesis of pyoderma gangrenosum.