Lexical inferencing is an important vocabulary learning strategy. Unfortunately, almost all research on this issue has been carried out in the reading context. This study is the first to directly measure lexical inferencing success in listening, by both native (N?=?47) and nonnative (N?=?30) speakers of English. It analysed the effects of contextual clue types, background knowledge, and L2 vocabulary knowledge on inferencing success. Results showed inferencing success rates of 59.6% (natives) and 35.6% (nonnatives), with success being significantly affected by the three variables. The study also measured L2 listeners' ability to notice unknown vocabulary in speech. This revealed limited noticing ability, indicating that a lack of noticing is likely to limit learners' inferencing opportunities and success.