Advanced maternal age at childbirth is a risk factor for the generation of trisomies such as Down syndrome because of the high frequency of non-disjunction at maternal meiosis 1. Thus, it is predicted that increased childbearing age is also relevant to the generation of maternal uniparental disomies caused by trisomy rescue or gamete complementation with a disomic oocyte produced through non-disjunction at maternal meiosis 1. Here, we report our molecular genetic data for 117 patients with Prader-Willi syndrome. The results indicate that advanced maternal age at childbirth is a predisposing factor for the development of maternal uniparental disomy 15 because of increased meiosis 1 errors. This notion is applicable to other maternal uniparental disomies as well, and provides useful insight into the occurrence of imprinting disorders after artificial reproductive technologies(ART). In particular, it is recommended to perform maternal age-matched comparison for the evaluation of the potential influence of ART on the development of maternal upd.