['the aim of this study was to determine the pattern of shrinkage after endovascular aneurysm repair (EAR) using logarithmic, exponential and linear models and to calculate a lag time is present.', 'patients with a complete CTA follow-up of 2 years and a primary shrinking aneurysm were included, resulting in a study group of 29 patients. Six functions, logarithmic, exponential and linear, all with and without lag time, were fitted to the thrombus volume obtained from measurements postoperative and after 6, 12 and 24 months. The correlation coefficient was used to determine the association between the calculated and measured values. A correlation coefficient >0.95 was considered a good fit.', 'a logarithmic model produced the best fits. From the 29 patients, two patients could not be described by any model. The remaining 27 patients could be fitted using a logarithmic function with a correlation coefficient of >0.95 (median 0.99, range 0.95-1.00). Twenty-two of these patients had a lag time (median 63.4 days, range 5.8-252.3). Only five of the initial 44 patients (11%) showed immediate sac shrinkage.'] Does the sac shrinking process after EAR start immediately in most patients?