The altarpiece of the church of Our Lady of the Elms, in Campo de Montiel, attributed to Francisco Cano, is a unique masterpiece that represents the essence of the Mannerism or Late Renaissance in the region. Its technical study is one of the objectives of this article that seeks to explain the constructive aspects and identify the materials (wood species, pigments and binders) and the techniques used. Simultaneously, we have characterized its current state of preservation, describing in detail the problems identified, both structurally and in terms of the polychromy. We have tried to revalue an important work that got to survive the events of the Spanish Civil War. Generally speaking, it is unpublished information that has been collected and presented here.