purpose: To define the clinical features and assess the frequency and causes of missed diagnoses of ruptured abdominal aortic aneurysm (AAA) in patients initially presenting to internists. patients: All identified patients with ruptured AAA presenting to internists during a 7 1 2-year period at a large academic medical center. methods: Chart review. results: We identified 23 patients with a ruptured AAA presenting to internists. Most had abdominal pain and tenderness, back or flank pain, and leukocytosis, whereas anemia and profound hypotension (systolic blood pressure below 90 mm Hg) were uncommon at presentation. In 14 cases (61%), the diagnosis of ruptured AAA was initially missed. Nine patients had an interval of 24 hours or more between presentation to the internist and surgery or death. The diagnosis was not made until after shock developed in nine patients who were hemodynamically stable at presentation. Of 17 patients who underwent surgery, 7 of 8 with preoperative shock died, compared with 2 deaths in 9 patients (p < .02) without shock. All six patients who did not have surgery died, yielding an overall mortality of 65% for the series. Ruptured AAAs were most frequently misdiagnosed as urinary tract obstruction or infection, spinal disease, and diverticulitis. Chart review revealed a general lack of physician awareness of the syndromes of contained rupture of AAA and symptomatic unruptured AAA. conclusions: In patients with ruptured AAA who present to internists, the diagnosis is often delayed or missed and this appears to adversely effect survival. Internists should familiarize themselves with the presentation and management of ruptured AAA.