To show a decrease of 60% in the incision hernia rate at 12 months(25% vs 10% incision hernias at 12 months)with a power of 80% and a significance level of 5%, investigators need 100 evaluable patients at 12 months in each arm. To compensate a 20% lost to follow up, we have to include at least 120 patients before the "principles training" and 120 patients afterwards. So the trial will end inclusions when 120 AAA patients have been entered using the Principles. Most likely the control group will be larger than these 120 patients,depending on the number of vascular surgeons participating in the teaching course and the timing of this course.