It is well known that task-irrelevant speech interferes with the retention of information in short-term memory, in particular when the to-be-remembered information is verbal and when the items are to be recalled in serial order. Much less is known about the effects of irrelevant sound on the interference with information from long-term memory, such as the semantic-associative networks leading to false memories. The aim of the present study is to test whether different types of background speech during encoding of semantically related word lists affect the occurrence of memory intrusions that were induced with the Deese-Roediger-McDermott paradigm. It was found across two experiments (one online and one in the laboratory) that irrelevant speech significantly increased the proportion of false recognitions of critical lures (i.e., words that were semantically associated with the lists), compared to noise or silence. In addition, unexpected sounds within the irrelevant utterances (an acoustical deviant or a taboo word) also affected the recognition of presented words, but there was no further influence on false memories. These results are consistent with attentional accounts of auditory distraction, postulating that any changes in the auditory environment capture attention from the focal task. In the present context, irrelevant speech may have diverted attention from the identity of to-be-remembered words (verbatim traces), thus leading to encoding of gist traces only, which produce false memories for associated words.