Purpose: To investigate the effect of age on voice fundamental frequency (F[subscript 0]) difference limen (DL) and identification of concurrently presented vowels. Method: Fifteen younger and 15 older adults with normal audiometric thresholds in the speech range participated in 2 experiments. In Experiment 1, F[subscript 0] DLs were measured for a synthesized vowel. In Experiment 2, accuracy in identifying concurrently presented vowel pairs was measured. Vowel pairs were formed from 5 synthesized vowels with F[subscript 0] separations ranging from 0 to 4 semitones. Results: Younger adults had smaller (better) F[subscript 0] DLs than older adults. For the older group, age was significantly correlated with F[subscript 0] DLs. Younger adults identified concurrent vowels more accurately than older adults. When the vowels in the pairs had different formants, both age groups benefited similarly from F[subscript 0] separation. Interestingly, when both constituent vowels had identical formants, F[subscript 0] separation was deleterious, especially for older adults. Pure-tone average threshold did not correlate significantly with either F[subscript 0] DL or accuracy in concurrent vowel identification. Conclusion: Age-related declines were confirmed for F[subscript 0] DLs, identification of concurrently spoken vowels, and benefit from F[subscript 0] separation between vowels with identical formants. This pattern of findings is consistent with age-related deficits in periodicity coding. (Contains 3 tables, 4 figures and 2 footnotes.)