This study investigates the link between breadth (or size) and depth of vocabulary knowledge, and the relationship between the latter and academic proficiency. Breadth of vocabulary knowledge was measured using a productive version of the Vocabulary Levels Test (Laufer & Nation, 1995), while depth was operationalised by productive knowledge of collocations. A small sample of 60 university students of English whose examination scores were closest to the 25th, 50th and 75th percentiles was selected. Relationships were determined between breadth of vocabulary knowledge and depth of vocabulary knowledge on the one hand, and between depth of vocabulary knowledge and academic proficiency (represented by examination scores) on the other. While a relationship between breadth and depth of vocabulary knowledge was found, suggesting a link between smaller vocabulary size and the production of deviant multiword units for the group as a whole, the relationship between depth of vocabulary knowledge and academic performance was not proved conclusively. It should, however, be kept in mind that numbers were relatively small. Further investigations using larger samples might find a more robust relationship.