Three experiments examined age-related differences in irrelevant-speech effects. Younger and older adults were required to recall short prose texts or lists of semantically related words presented visually together with distractor speech. In all experiments, older adults made more semantically related intrusion errors from the irrelevant speech than younger adults. Results of a source memory test suggested that these age-related differences in interference are most likely due to both inhibitory deficits and source-monitoring problems. The results lend partial support to the inhibition deficit theory of cognitive aging.