This study investigated the receptive vocabulary growth of advanced EFL learners in an English-medium degree programme. The study used the Vocabulary Size Test in a cross-sectional design to measure the vocabulary size of learners at various stages of study. The effect of word frequency on vocabulary development and the presence of an implicational scale among frequency levels were also investigated. The results of the study suggest that learners' vocabularies expand by about 500 words a year. However, there is evidence for severe attrition in the final year. Frequency is a significant factor in receptive vocabulary development, but an implicational scale could not be established.