Mercer Island High School (MIHS) is a public high school located in Mercer Island, Washington, United States, as part of the Mercer Island School District. As of the 2018–19 school year, the school had an enrollment of 1,552 students and 77.5 classroom teachers (on an FTE basis), for a student–teacher ratio of 20.0:1. There were 44 students (2.8% of enrollment) eligible for free lunch and 13 (0.8% of students) eligible for reduced-cost lunch.