Introduction: Aortic mechanical function was an independent predictor of aortic dilatation in Marfan. Patients (pts) operated for aortic dissection remain at risk of late complications, namely aneurysm and rupture of the residual aorta. Purpose: The aim of this study was to assess the prognostic influence of aortic mechanical function indexes, evaluated by magnetic resonance (MR) on the late evolution of operated aortic dissection. Methods: We studied 47 consecutive pts operated for type A aortic dissection (ascending aorta graft in all pts, aortic valve re-suspension in 16 and aortic valve prosthesis in 14), 26 men, aged 53.8 ^ 11.1 years old. All were submitted to magnetic resonance imaging (MRI) two months after surgery and afterwards, annually, for three years. MR study: GE Signa 1.5T; high resolution spin-echo and cine MR. For analysis, residual aorta was divided in 3 segments: 1-arch; 2-descending thoracic; 3-abdominal. In order to assess long-term evolution, we evaluated segments dimensions and presence of residual flap, at initial and follow-up studies. Mechanical function indexes were obtained at the initial evaluation: 1. Pulse pressure (mmHg); 2: Segmental indexes—area strain; distensibility (dynes/cm); elastic modulus (dynes/cm 2 1); beta stiffness index. Aortic aneurysm were considered when the dimension of a thoracic segment was .49 mm and abdominal .39 mm. Results: Mean follow-up was 39.5 ^ 0.56 months. No patient had aneurysm on early evaluation. A group of 23 pts had a residual flap. Complications detected: aneurysm development in 35 segments, from 22 pts. Mechanical function influence: 1. Pts with aneurysm in any segment had higher pulse pressure than pts without aneurysm (57.8 ^ 4.4 vs 41.6 ^ 3.8, p 1⁄4 0:000); 2. Pts with aneurysm in segment 1 had lower strain (7.4 ^ 1.7 vs 19.1 ^ 1.7, p 1⁄4 0:000), lower distensibility (0.35 ^ 0.11 vs 0.83 ^ 0.08, p 1⁄4 0:000) and higher beta stiffness index (0.9 ^ 0.3 vs 0.5 ^ 0.1, p 1⁄4 0:003); 3. Pts with aneurysm in segment 2 had lower strain (11.6 ^ 1.7 vs 23.6 ^ 1.1, p 1⁄4 0:000), lower distensibility (0.47 ^ 0.08 vs 1.25 ^ 0.11, p 1⁄4 0:005), higher elastic modulus (5.6 ^ 0.8 vs 2.6 ^ 0.2, p 1⁄4 0:004) and higher beta stiffness index (0.71 ^ 0.08 vs 0.35 ^ 0.05, p 1⁄4 0:000); 4. There was no association between the development of aneurysm in segment 3 and mechanical indexes. 5. In the subgroup of pts without a residual flap (25 pts) there was a more significant difference between mechanical indexes of segments with and without aneurysms. Conclusion: Pts operated for aortic dissection had a high incidence of late aneurysm development. This complication was associated with indexes of higher aortic stiffness at early evaluation. This knowledge may influence the follow-up strategy of this aorthopaty.