Five patients with systemic lupus erythematosus (SLE), four of whom died with colonic perforations, are reported. Perforation of the colon constituted the most frequent cause of death among 107 patients with SLE admitted to the Rheumatic Disease Unit during a three year period. All five patients with colonic perforation had clinical and laboratory manifestations of active SLE in addition to the abdominal syndrome. Most striking was evidence of active arteritis in all patients with either central nervous system involvement and/or peripheral arteritis, in addition to that found in the gastrointestinal tract. Hyperglobulinemia and rheumatoid factor as well as antinuclear antibodies were present at some time in all patients. The abdominal syndrome was characterized by the insidious onset of lower quadrant pain which was intermittent and colicky. Although direct abdominal tenderness was eventually present in all patients, rebound tenderness and hypoactive bowel sounds were variable and abdominal rigidity occurred only in one patient and late in the course. The differential diagnosis of abdominal pain in SLE is reviewed and possible mechanisms for the production of colonic perforations are discussed. It is suggested that the presence of rheumatoid factors in conjunction with circulating immune complexes may be the pathogenetic mechanism via the production of a mesenteric arteritis.