The monastery of San Andrés de Arroyo (established in 1181) is one the best examples of Cistercian architecture in the Spanish region of Castilla y León. In this study, strontium isotope ratios were used to study the population of the recently excavated graveyard of this monastery. Twenty-nine individuals (of which 13 had preserved teeth) found in burials from the 13th and 14th centuries were subjected to analysis. Enamel 87Sr/86Sr ratio values obtained by using a multicollector ICP-MS instrument were used to distinguish between local and nonlocal individuals. Additionally, an anthropological study based on entheseal changes and other paleopathological conditions was carried out in all the exhumed individuals. This combined data allowed us to define the chemical and osteological diversity of a Medieval Spanish monastery and its surrounding village. Among the usual profiles for a rural society