The purpose of this study is to analyse the diachronic variation in the skeletal sample exhumed from the medieval necropolis of Sant Pere Churches, interpreting the results using the archaeological and historical evidence. The Sant Pere Churches are a monumental Romanic complex located in Terrassa (Spain) and built over the earlier Episcopal Cathedral of Egara from the Visigoth period. Egara has traditionally been considered the precursor of the current city of Terrassa; however this name disappeared from historical documentary sources after the period of Muslim incursions into Hispania (8th century). An archaeological excavation undertaken recently at the Sant Pere Churches provided us with the opportunity to study the population that was interred in this complex during that epoch. In total, the skeletal remains of 208 individuals were examined. In order to analyse the diachronic variation, the sample was divided into two periods, that of the Cathedral of Egara (4th–8th centuries; N = 128) and that of the Parish Churches of Terrassa (9th–13th centuries; N = 80). Both periods of the complex exhibited a similar skeletal age distribution, including under-representation of non-adult individuals. Nevertheless, a bias towards males in terms of sex distribution, sex differences in the mortality level and greater sexual dimorphism were observed in the population interred at the Cathedral of Egara. Moreover, analysis of the prevalence of skeletal disorders also provided evidence of higher differences between sexes for the period of the Episcopal Cathedral of Egara, the female population exhibiting the lower prevalence. Additionally, diachronic variation in both postcranial and dental disease patterns was observed, suggesting different activity patterns and food consumption between the periods. Overall, the results suggested that diachronic osteological variation observed in the Sant Pere Churches skeletal sample was most probably linked with the changes in the role of the complex following the Muslim incursion of the 8th century. Copyright © 2009 John Wiley & Sons, Ltd.