Contribution: This study examines the influence of English as the medium of instruction (EMI) in the engineering college of a public university in a non-native English-speaking country, Saudi Arabia. The study analyzes alumni grade-point average (GPA) records and their English proficiency levels at the first year according to their transcripts. Also, this research contributes to the literature through its analyses of the current students' attitudes, societal attitudes, and self-efficacy regarding students' preferred language of instruction. Background: This study seeks to fill a gap in the literature, as most studies on EMI policy focus on teaching approaches and interaction modes. Research Question: What is the effect of the EMI policy on the performances and attitudes of engineering students? Methodology: The research uses three instruments to collect data: (1) engineering college alumni records; (2) current student questionnaires; and (3) engineering instructor questionnaires. Findings: Students' English proficiency in their first-year correlates significantly with GPA, thus predicting the overall GPA upon completing their five-year programs. The results of the survey of the current students' attitudes correlate with their preferred medium of instruction. Most of the students prefer their native language, Arabic, as the language of instruction. However, the engineering instructor survey reveals that most instructors believe that the EMI policy does not affect students' abilities to participate in classroom activities and examinations. Thus, there is a contradiction between students' and instructors' perspectives. It is recommended that engineering program policymakers consider the contrast in students' and instructors' perspectives on EMI when designing programs.