The type and amount of information that may be derived from osteoarchaeological samples is directly related to the state of preservation of the remains. By quantifying the state of preservation of osteoarchaeological samples it is possible to better determine the discrepancies between the “osteological sample observed” and the “original population it represents”. In this study, the state of preservation has been evaluated using two preservation indexes: one quantitative (the Anatomical Preservation Index, API) and the other qualitative (Qualitative Bone Index, QBI). Seven samples, comprising a total of 768 individuals were analysed. The results of this investigation demonstrate how the state of preservation may have an impact on anthropological observations. In particular: 1. the MNI evaluation is closely related to the preservation and fragmentary state of the osseous remains; 2. the state of preservation is age-dependant and produces an under-preservation of sub-adults individuals; 3. the bone fragmentation and the alteration of cortical surfaces can bias palaeopathological prevalence.