The ‘maternal age effect’ in human reproduction, characterized by a negative relationship between maternal age and reproductive efficiency, remains a poorly understood phenomenon. Current data suggest that oocyte physiology determines this relationship. In this review, we present a hypothesis of a mitochondrial role in the physiology of ageing in human oocytes. We suggest that the efficiency of oxidative phosphorylation in the ageing human oocyte is degraded by free radical attack on the primordial oocytes residing in the ovary. Although deficiencies in oxidative phosphorylation can be accounted for in the short term by anaerobic respiration, we suggest that, in the long term, the level of oxidative phosphorylation strongly influences oocyte quality.