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This small-scale study investigates (a) whether academic vocabulary compares in development with vocabulary breadth and depth for Iranian ESP/EAP learners and, if the answer is positive, (b) whether this trend of development happens across proficiency levels. Fifty-seven graduate students served as the subjects who were also divided into high and low groups based on whether they had acquired the most frequent 2,000 words. Multiple regression analysis results show much shared variance between breadth and depth tests, and academic vocabulary test for the participants as a whole group. Therefore, as learners’ vocabulary breadth and depth increase, so does their academic vocabulary. A similar finding is also observed for the high group and low group. However, the finding for the low group is contrary to our expectation. The results suggest more systematic vocabulary development for the high group, less for the participants as a whole group, and least in the low group. This investigation has some implications for language, and more particularly vocabulary, instruction for ESP/EAP purposes in Iran.