The records of 106 consecutive patients referred to the University of Colorado Medical Center (UCMC) vasculitis study group during a 5-yr period were evaluated for gastrointestinal (GI) manifestations attributable to vasculitis. There were 3 groups: 18 with leukocytoclastic vasculitis (LCV) on skin biopsy younger than 16 yr of age; 75 with LCV older than 16 yr of age; and 13 with polyarteritis nodosa (PAN). Significant GI manifestations at presentation or exacerbation of vasculitis occurred in 38 of 106 (36%) patients. These were more frequent in LCV patients younger than 16 yr (66%), than older LCV patients (26%) or PAN patients (46%). The commonest complaint was abdominal pain (79%), followed by nausea (63%), vomiting (37%) and diarrhea (23%). GI bleeding was present in 52% and acute abdomen in 21% of patients. No consistent radiologic findings were noted. Duodenal and peritoneal biopsies suggested vasculitis in 6 LCV patients. Seven exploratory laparotomies were performed in 4 LCV and 3 PAN patients. Intestinal infarction was found in 3 patients with PAN, but in one of the LCV patients. Two patients with LCV with an acute abdomen were not explored and responded promptly to iv corticosteroids. Thus, systemic vasculitis frequently involves the GI tract. In patients with LCV, recognition of this association and treatment with corticosteroids can avoid surgery. In our patients with PAN, however, acute abdominal signs indicated infarction requiring surgery and resection.