Studies manipulating emotional valence in prospective memory (PM) have so far revealed inconsistent results. In the present study, two experiments were conducted to systematically disentangle the effects of varying emotional valence in the encoding versus retrieval phase of PM in older adults. Results showed that, while cue valence at retrieval had no influence on PM performance, at encoding both positive and negative valence resulted in reduced PM performance. Findings suggest that emotional valence may have an influence on mnemonic processes at encoding rather than modifying cue detection in aging.