A 65-year-old woman presented with widespread necrotising cutaneous ulceration and oral involvement. Past history included rheumatoid arthritis, and a left nephrectomy.Examination revealed multiple violaceous undermined ulcers. Blood investigations showed an acute inflammatory response. Skin histopathology showed epidermal ulceration with acute and chronic inflammation. Direct immunofluorescence was negative. A diagnosis of pyoderma gangrenosum with oral involvement was made. Mycophenolate mofetil therapy resulted in complete resolution of her pyoderma gangrenosum. Her treatment was complicated by a left proteus mirabilis psoas abscess. This resolved following four weeks of antibiotics.Pyoderma gangrenosum with oral involvement is rare but has been linked with inflammatory bowel disease and hematological disorders. Oral pyoderma gangrenosum has not previously been described in rheumatoid arthritis. Primary psoas abscess is rare but can develop in immunocompromised patients. Proteus mirabilis has been reported in patients years after nephrectomy. This is a rare case of pyoderma gangrenosum with oral involvement.