The clinical and laboratory features of three patients with systemic inflammatory complications following jejuno-ileal bypass surgery for morbid obesity are described. The constellation of an asymmetrical polyarthritis, tenosynovitis, sterile skin pustules, mucous membrane ulceration and retinal vasculitis resembled Behçet's syndrome. Serum complement levels were normal and circulating immune complexes not regularly detected, although hypocomplementaemia, elevations in Clq and rheumatoid factor binding materials were noted prior to clinical relapse in one patient. Antibiotic therapy proved disappointing, whereas dapsone produced a sustained remission. Bacterial overgrowth was not invariably found which together with recurrence of symptoms following bypass reversal, suggest that bacteria may only be required to initiate, not perpetuate inflammatory complications.