Despite the vast research on test anxiety and test performance since the 1950s, studies on how students' English test anxiety affects their English proficiency test performance in the context of second- and foreign language learning remain few. Therefore, using a quantitative research design, this study explored students' English test anxiety and proficiency test results of students at an autonomous university in Thailand. The study was focused on examining the distinctive constructs and levels of English test anxiety, along with the variations by gender and proficiency level. It also examined the correlation and predictive power of EFL students' English test anxiety towards their English proficiency test performance both in general and specific skills. The results showed that university students in Thailand had a high level of English test anxiety, which had a detrimental impact on their English proficiency test results. "Worry, tension, emotionality," and "bodily/physical symptoms" were four distinct constructs that characterized their anxiety over the English exam. "Worry" was the strongest construct in lowering students' overall and individual English test performance. Female and low-proficiency students, in particular, had to deal with high levels of test anxiety, and they were especially apprehensive before English tests. These findings should encourage English educators and policymakers to develop strategies for generating welcoming situations and environments for students prior to their English tests, as well as to implement an appropriate treatment plan incorporating cognitive and behavioral therapies. It is advised that teaching and testing materials not only concentrate on conveying cognitive knowledge and strategies for answering test questions, but also include tools that may be used to manage real-world exam anxiety.