A 74-year-old man with pain and swelling of the left thigh was transferred from another hospital for further investigation. On admission, a diagnosis of a left femoral vein thrombosis was made and he continued on anticoagulant therapy. However, three and a half hours after admission he suddenly developed hypotensive shock and became unconscious. Rupture of a peripheral aneurysm was suspected in view of a rapid fall in the hematocrit and the images of vascular echography. Rupture of a left popliteal aneurysm was specifically diagnosed following intraarterial digital subtraction angiography. An emergency aneurysmectomy and vascular reconstruction using the great saphenous vein was performed. Interestingly, Klebsiella pneumoniae was cultured from both the wall of the left popliteal artery and the wound. Antibiotic therapy was therefore changed to flomoxef (FMOX) on the 5th postoperative day (POD 5) and treatment continued for a total of 6 weeks in accordance with the therapy of infectious endocarditis. He returned to the previous hospital on POD 61.