This study examines whether unfamiliar proper names affect English as a second language (ESL) learners' listening comprehension. A total of 110 intermediate to advanced ESL learners participated; comprehension of a short news text was tested under two conditions, Names Known (all proper names pre-taught in advance) and Names Unknown (all proper names unfamiliar prior to listening). The Names Known group performed significantly better than the Names Unknown group on two measures, true-false-don't know statements and open-ended questions. The effect of unfamiliar proper names on comprehension remained statistically significant after the listening proficiency variable was controlled. Listeners in the Names Unknown treatment were able to derive 44.8% of information about the referents of proper names from context but they could not identify all the referents successfully. Unfamiliar proper names evidently hinder comprehension, which was also supported by the participants' task difficulty ratings. When proper names were familiar, participants rated all comprehension tasks as easier to do and self-reported higher comprehension success. In contrast, when proper names were unfamiliar, participants rated all comprehension tasks as harder to do and self-reported a lower amount of comprehension. It has long been established that vocabulary knowledge is a prerequisite to successful comprehension. This study confirms that, similarly to common vocabulary, the presence of unfamiliar proper names decreases the ESL learners' chances of understanding spoken English. Implications of the findings for second language learning and testing are discussed. It is recommended that teachers be flexible when setting up listening exercises and use different techniques depending on the depth of understanding the learners are supposed to achieve. If the instructional goal is listening for gist, proper names will unlikely affect the outcomes of the activity. However, if detailed and precise understanding is required, then it is unrealistic to expect ESL listeners to cope with unfamiliar proper names "on the spot" without assistance or preparation. It is also advisable to avoid unfamiliar proper names in a testing situation because they may cause unwarranted anxiety and reflect negatively on the ESL listeners' performance. (Contains 10 tables.)