Accurate memory retrieval from partial or degraded input – such as recognizing a person when they have drastically changed their hairstyle – requires the reactivation of memory traces, via a hippocampal-based mechanism known as pattern completion. Given its extensive excitatory recurrent connections, sub-region CA3 within the hippocampus has been identified as a likely candidate to execute the auto-associative processing essential for pattern completion (Marr, 1971).Age-related changes in hippocampal integrity have been hypothesized to shift the balance of memory processes in favour of the retrieval of previously stored information (pattern completion), to the detriment of encoding new events (pattern separation). In this study, we (i) established a novel paradigm providing a behavioural marker for hippocampal pattern completion, and (ii) examined how memory retrieval, and the process of hippocampal pattern completion in particular, is affected by cognitive aging.Healthy younger and older adults were required to identify previously learned scenes among new ones. Additionally, all stimuli were presented in gradually masked versions to alter stimulus completeness. For both groups, recognition accuracy was reduced with decreasing stimulus completeness. This effect, however, was much more pronounced in older adults, suggesting that pattern completion is adversely affected by aging. Intriguingly, despite this substantial age-related performance decline, when novel scenes were shown, only the older adults showed an increased tendency to identify these as familiar scenes – revealing a clear bias toward pattern completion.These results provide much needed empirical support for theoretical models of age-related changes in hippocampal function, and inform our understanding of (i) how partial information influences recognition memory (i.e. pattern completion), (ii) how cognitive aging shifts mnemonic processing in favour of the retrieval of previously stored information and to the detriment of encoding new events, and (iii) how age-related memory impairments can be understood in the context of environmentally aided (recognition) vs. more self-initiated (free recall) processing.