A 70-year-old man presented with haematuria and restrictive urinary symptoms 7 years after a transurethral prostatectomy (TURP). Onset of symptoms coincided with development of a large skin ulcer on his back. A diagnosis of pyoderma gangrenosum was made based on clinical signs and histopathology. On repeated cystoscopy the urethral sphincter was obliterated by necrotic tissue, suspicious for malignancy. Histopathology revealed only necrotic tissue consistent with infarction of the prostate and sphincter. This clinical presentation with infarction of the prostate and sphincter, concurrent with development of skin ulcers, was consistent with pyoderma gangrenosum affecting the prostatic urothelium and sphincter. Previous prostatic surgery may have predisposed our patient to development of pyoderma gangrenosum in the area of the prostate.