BACKGROUND Gastrointestinal haemorrhage associated with a primary aorto-enteric fistula (PAEF) is potentially lethal. The aims of this study were to discuss the gastrointestinal characteristics of PAEF, to identify associated laboratory findings and to discuss pitfalls in pre-operative diagnostics. METHODS Medical and surgical charts of patients with PAEF. RESULTS Individuals with PAEF (n = 7, 68 +/- 5 years) presented with multiple episodes of haematemesis (n = 5) and/or melaena (n = 6), all in the presence of aneurysmatic aortas (5.4 +/- 1.0 cm). Laboratory testing reflected a state of acute (C-reactive protein, CRP, 94 +/- 12 mg/ml; leucocyte counts, 12.0 +/- 1.0.10(9)/L) and chronic inflammation (erythrocyte sedimentation rate, ESR 52 +/- 5 mm/hr). Prior to operation, a gastroduodenoscopy correctly diagnosed only one PAEF patient and CT scans identified 3. Two patients exsanguinated in a two-week waiting period prior to corrective surgery. CONCLUSIONS Recurrent gastrointestinal blood loss in the presence of an aneurysm requires urgent gastroduodenoscopic evaluation. Computer tomography is sensitive in providing direct or circumstantial evidence of a fistula. A combined acute and chronic inflammatory state associated with PAEF is reflected by elevations of CRP and ESR. A PAEF is a unique form of ruptured aneurysm, and this entity mandates imminent radiological and surgical consultation aimed at instituting aggressive treatment within hours.