This article reports the results of two studies on the vocabulary growth of advanced learners of English as a foreign language in an English-medium degree programme. Growth in learners' written receptive and productive vocabularies was investigated in one cross-sectional and one longitudinal study over three years. The effect of word frequency on vocabulary development and the growth in academic vocabulary were also investigated. The overall results of the two studies suggested that learners' receptive vocabularies did not grow significantly, whereas the longitudinal data indicated expansion of productive vocabularies by about 10%. Both receptive and productive knowledge of academic vocabulary improved significantly in the longitudinal data. Frequency seemed to have a stable overall effect in vocabulary development. However, evidence for an implicational scale among the frequency levels was obtained only for the receptive test.