||Establishing age-at-death is important to forensic and biological anthropologists for identification and demographic analyses, but some degree of error is unavoidable. In human osteoarchaeology, there is a general assumption that there is worse preservation with increasing age of adult skeletal remains resulting in inaccuracies in paleodemographic reconstructions. This thesis examines skeletal material from the 17th to 19th-century Middenbeemster cemetery in the Netherlands to understand taphonomic processes that cause age and sex biases in the preservation of the adult pelvic girdle. Skeletal age estimation techniques have focused on the iliac auricular surface and pubic symphysis. However, the morphological features that are considered for age estimation methods of the pubic symphyseal surface, iliac auricular surface, and sacrum get destroyed or damaged to the point where the morphological features are no longer or only partially observable, which, in turn, affects the accuracy of these age estimation methods. The degeneration pattern in human remains from individuals aged 50 years and older becomes too unclear to put into smaller age groups, which is further complicated by taphonomic factors. Differences in bone preservation are caused by several taphonomic processes that affect the pelvic girdle of old adults more than young and middle aged adults. The general results show that the pelvic girdle of old adults is less well-preserved than young and middle adults, and that adult female pelvises are less complete than males. This research supports the view that age biases in preservation are more important than sex biases.