Summary: Lexical stock, i.e. the sum of vocabulary, is an essential part of the context of learning any second language; without it, language skills (listening, reading, speaking and expression) cannot be developed. Accordingly, this study investigates the size and depth of lexical stock, and its relationship to the general proficiency level of learners of English as a foreign language. The study sample included 120 students from the University of Bahrain. The sample was randomly selected from intermediate and advanced level students. The study mainly aims to answer four questions: What is the effect of general linguistic proficiency on the size of the received and produced vocabulary of English language students at the University of Bahrain? How does general linguistic proficiency affect the depth of the lexical stock of English language students at the University of Bahrain? What is the relationship between received and produced vocabulary on the one hand, and the depth of lexical stock on the other hand? What is the relationship between the size of vocabulary and the nature of the lexical network? The students were subjected to three lexical tasks. The first two tasks were the Task, Lex30 Association (Word) test (Paul Meara and Eurocentres, 1990), which aims to measure vocabulary size, and the Jones exercise (Fitzpatrick and Meara, 2000), which aims to measure word association. The third task was for students to perform the Gyllstad's Collex Test (2007), which aims to explore the depth of lexical stock. The study adopted the quasi-experimental approach by following a quantitative approach in data analysis. The study data were analyzed by comparing the results of the two groups obtained from the three tasks using SPSS version 16.0. The study resulted in the following: General language proficiency had a positive effect on the size of students' received vocabulary, a moderate effect on the size of their produced vocabulary, and a very low effect on the depth of lexical stock. No relationship was found between vocabulary size and the nature of the lexical network. Based on these results, some educational recommendations and others regarding future research were made.