The authors report a case of retroperitoneal perforation of a duodenal ulcer. This is a rare condition which is exceptionally responsible for abscess formation. If often has a poor prognosis. In the present case, the abscess was infrahepatic. The diagnosis of the origin of the abscess was established by radiological opacification via percutaneous puncture. Surgical drainage and irrigation performed via an extraperitoneal approach centered over the cavity, combined with triple-agent antibiotic therapy (penicillin, gentamicin, metronidazole) ensured collapse followed by sterilisation of the abscess cavity. The ulcer was cured by medical treatment. This case differs from the published case in terms of the diagnostic procedures classically used (upper gastrointestinal endoscopy and small bowel series), the infrahepatic site of the abscess and the extraperitoneal surgical treatment which avoided dissemination to the peritoneal cavity.