Grossmont High School is a public high school in eastern San Diego County, California. Opened in 1920, it is the oldest public high school in East County and the first of twelve high schools currently in Grossmont Union High School District. The school has an approximate enrollment of 2,800 students.

Grossmont High School has been accredited by the Western Association of Schools and Colleges (WASC) since 1962. It was recognized as being a California Distinguished School for the scholastic year of 2008–2009.

The school's mascot is the Foothiller, so chosen because, at the time of the school's construction, East County was much more isolated from the rest of San Diego than it is today and was often referred to as the boondocks or the foothills.