"Pincus," a nine year old male castrated Shih Tzu presented to the Cornell University Emergency Service for a suspected cutaneous reaction to trimethoprim-sulfa. He had, over the previous month, received two courses of TMS for bilateral anal sac abscesses, from which the resistant bacteria Stenotrophomonas maltiphilia was cultured. On presentation, Pincus had moist, ulcerative lesions covering 75% of his body, most notably perioral, periaural, periocular, on his muco-cutaneous junctions, and his ventral abdomen. He was initially managed with pain medication (fentanyl, ketamine) and because he was severely neutropenic with a degenerative left shift, broad spectrum antibiotics (ampicillin sulbactam, enrofloxacin). Histopathology of skin biopsies was consistent with immune-mediated vaculitis secondary to antigenic stimulation. Pincus was treated with immunosuppressive doses of dexamethasone and prednisone, aspirin for hypercoagulability, and pentoxifylline for its rheologic properties. Pincus responded well to treatment and was discharged ten days later. In follow-up exams, all dermatologic, hematologic, biochemistry and ultrasound abnormalities had resolved.