A characteristic intermittent neutrophilic dermatosis, associated with polyarthritis, tenosynovitis, malaise, fever, and cryoglobulinemia, occurs in 20% of patients who undergo ileojejunal bypass surgery for the treatment of morbid obesity. The clinical syndrome may mimic gonococcal sepsis. The histologic changes in the skin are those of Sweet's syndrome. The syndrome remits spontaneously in most cases, but it may recur intermittently over a period of years. Treatment with low-dose steroids, tetracycline, or metronidazole suppresses symptoms in most cases, and restoration of normal bowel anatomy is curative. Skin testing with Streptococcus pyogenes antigen causes an exacerbation of symptoms, or may provoke the entire syndrome de novo. Bacterial peptidoglycans, especially those of group A streptococci, produce similar arthritis and skin lesions in animal models. Peptidoglycans from numerous intestinal bacteria share common structural and antigenic features with S. pyogenes peptidoglycan and are suggested as causative of the toxic and immunologic features of this syndrome.