This study assessed Malaysian tertiary students' levels of passive and controlled active vocabulary knowledge. Two tests from the Vocabulary Levels Test were used to collect the data namely the Passive Vocabulary Test and Controlled Active Vocabulary Test. When using the test, the researchers were not particularly interested in the students' total score on the tests, but were interested more in whether the students knew enough of the high-frequency words. 360 first- and second-year university students from five diploma programs were involved in the study. The findings revealed that majority of them did not have enough vocabulary knowledge and vocabulary size to use English as their second language though formal exposure to the language had been given to them for more than 12 years. This paper, besides discussing the students' levels of passive and controlled active vocabulary knowledge and their vocabulary size, highlights the vocabulary levels and vocabulary size they should attain. The probable impact vocabulary knowledge has on the acquisition of other English language skills is another area discussed. Some recommendations for teaching approaches are also put forward.