Krashen (2004) has advocated that narrow reading, i.e., reading a series of texts addressing one specific topic, is an effective method to grow vocabulary. While narrow reading has been championed to have many advantages for L2 vocabulary learning, there remains a relative dearth of empirical studies that test the impact of narrow reading on L2 learners' lexical growth. The present study examines whether narrow reading results in L2 vocabulary learning. A total of 61 high intermediate learners read a series of texts either thematically related (narrow) or unrelated (wide) over one month. The findings showed that narrow reading considerably facilitated learners' understanding of meanings of target words and their ability to appropriately use them. The narrow group's responses to an exit questionnaire revealed several factors that could have accounted for this improvement in their vocabulary knowledge. Several implications for vocabulary teaching are discussed.