The present study addressed the role of speed as a factor in tests of second language (L2) vocabulary knowledge, presupposing that speed of performance is important in actual language use. Research questions were: (a) Do learners with a larger vocabulary size answer faster on an L2 vocabulary breadth test than smaller vocabulary sized learners?; (b) Are there systematic increases in response time (RT) as word frequency decreases in an L2 vocabulary breadth test?; and (c) Do RTs of correct responses on an L2 vocabulary breadth test predict accurate and quick L2 reading? Participants were 24 Japanese university students. Results indicated that (a) vocabulary size facilitated lexical accessibility, (b) high frequency words were accessed more quickly but this was only observable after reaching a certain threshold of vocabulary size, and (c) vocabulary score (accuracy) alone was not associated with accurate and quick reading but vocabulary RT (accuracy + speed) was.