Little is known about the role of serum and tissue mediators in the progression of ascending aortic aneurysms and dissections. We examined how the tissue expression of microRNAs and matrix metalloproteinases (MMPs), as well as the serum levels of osteoprotegerin, adiponectin, and high sensitivity C-reactive protein (hsCRP) are associated with these entities. We enrolled 21 patients with ascending aortic aneurysm, 11 with acute Stanford type A aortic dissection and 18 controls. The serum levels of osteoprotegerin, adiponectin, and hsCRP, as well as the tissue expression of MMPs 2 and 9 and tissue microRNAs 29 and 195 were compared among groups. There was no difference regarding serum osteoprotegerin, adiponectin, and tissue MMP2 and MMP9 levels. hsCRP was higher in the dissection group (P = .03). Tissue expression of microRNA 29 was 2.11-fold higher in the dissection (P = .001) and 2.99-fold higher in the aneurysm group (P < .001), compared with the control group. Tissue expression of microRNA 195 was 2.72-fold higher in the dissection (P < .001) and 2.00-fold lower in the aneurysm group (P = .08), compared with to the control group. These findings support the contribution of microRNAs in the progression of aneurysm formation and dissection, suggesting a role as potential biomarkers and future therapeutic targets.