Vascular complications and arterial hypertension are major risk factors in the evolution of disease connected with coarctation of the aorta. Supra- and sub-stenotic aortic aneurysms are classical findings, whereas a dissecting aneurysm is a rare occurrence. In this study, we report on a case of acute dissection of the ascending aorta complicating a poorly followed-up coarctation of the aorta in a ten-year-old girl. The diagnosis, determined by X-ray of the thorax, was confirmed by echocardiography and magnetic resonance imaging. The first operative stage consisted of treating the aneurysm. After resection of the latter, an impregnated dacron prosthesis was inserted in termino-terminal. The immediate result is satisfactory, and a second operation is planned for the aortic coarctation.