Upon its arrival at the centre, Matrimonio místico de Santa Catalina de Alejandría y San Sebastián was in a poor state of conservation that prevented us from seeing what the experts sensed to be a fine work. Numerous previous interventions had damaged and altered the paint layer; manipulation of the support had resulted in severe deformations, and the original format of the work had been modified following the addition of two strips of canvas at the top and bottom. All this, together with other defects caused by its poor state of conservation, greatly hindered the reading of the original piece. During the restoration process, the perimeter of the painting was protected in order to prevent a greater number of detachments; the canvas additions were removed, and the remains of dirt were cleaned using an aqueous solution with a neutral pH. Once clean and returned to its original size, the canvas was transferred to a custom-made stretcher frame; after the new stretching, a layer of Dammar varnish was applied prior to the pictorial reintegration work, this being one of the most complex phases of the intervention. The differences between the work that arrived at the centre and the restored version are clearly visible. After the intervention, Matrimonio místico de Santa Catalina de Alejandría y San Sebastián has recovered not only its chromatic richness but also all the details and traces of the fine original work, lost in inappropriate and unfortunate interventions that had disfigured the appearance of its figures and altered the format conceived by the author himself. The work carried out reveals an exceptional piece of facture that fully meets the quality standards of the Italian school.