Recently researchers have proposed using information from teachers and learners to supplement the information from corpora in the selection of the most useful words for foreign language learners. Yet the extent to which these data sets correlate to one another is unclear. This study explicitly investigated the relationships between (a) the lexical coverage in 18 corpora, (b) the knowledge of 275 Vietnamese English as a foreign language (EFL) learners, and (c) the perceptions of 78 EFL teachers of the usefulness of 973 high-frequency words. The correlations between lexical coverage and the other two factors were significant but small, and the correlations between learner vocabulary knowledge and teacher perceptions were large. Teacher perceptions better-predicted learner knowledge than lexical coverage. This study confirms the value of lexical coverage as a key criterion to select words for foreign language learners, and also highlights the importance of teachers' perceptions of usefulness on ultimate vocabulary learning in EFL contexts.