Pyoderma gangrenosum is a rare, ulcerative, cutaneous condition. First described in 1930, the pathogenesis of pyoderma gangrenosum remains unknown, but it is probably related to a hyperergic reaction. There are various clinical and histological variants of this disorder. Pyoderma gangrenosum often occurs in association with a systemic disease such as inflammatory bowel disease, rheumatologic disease, paraproteinaemia, or haematological malignancy. The diagnosis, mainly based on the clinical presentation and course, is confirmed through a process of elimination of other causes of cutaneous ulcers. Local treatment may be sufficient for mild disease, while for severe cases, systemic immunosuppressants are the mainstay. Long-term treatment with these agents is often required, but this can expose patients to adverse side-effects.