This paper describes the methodology followed in the conservation and restoration of the panel “Saint Sebastian calling on the faith of the Christian captive brothers Marcus and Marcellianus”, datable to the late sixteenth century, belonging to the ancient altarpiece in the presbytery of the Church São Sebastião (Saint Sebastian), Terceira Island, Azores, and currently at the Museum of Angra do Heroísmo. It begins by presenting an historical overview and an iconographic and artistic study of the panel, which proved crucial to the understanding of the subject and its setting at the time, the church and the whole altarpiece. The double meaning as a testimony of faith and a symbol of national identity in times close to or already in the process of loss of independence from Portugal, is achieved through the hagiographic representation of the patron saint of the church on a base of cedar wood (Juniperus brevifolia), which enables to infer an author or local production. In the late nineties of the twentieth century, this support showed an intense deterioration resulting from colonization by fungi (brown rot) and previous interventions. The work done back than was held by various thinning of the wood and partial filling that allowed the restoration of the physical balance of each one of five boards and the panel as a whole. After this phase, the intervention was stopped, coming to resume in 2007, with the further stabilization of wood, reassembly, repainting survey and treatment of pictorial layer. The methodology was adapted to the most current criteria, keeping only what had once been widely followed in the areas affected by fungal action, with a clear structural instability and inability to recover only by consolidating.