Abdominal aortic aneurysm is operated when the size is more than:
Ref. Sabiston Textbook of Surgery. Pg. 1723
 
INDICATIONS FOR OPERATION
Asymptomatic –

Aneursym  >55mm in anteroposterior diameter.
Patient fit for surgery (expected mortality rate <5%)
Indications for endoluminal operation are the same as for open operation .

Symptomatic .

Aneursym of any size that is painful or tender
Aneursym of any size that is causing distal embolisation .
Indications are wider than for an asymptomatic lesion (expected mortality rate 5-20%)
35 mm
45 mm
55 mm
65 mm