Medical Lake is a city in Spokane County, eastern Washington, United States. At the 2010 census, the population was 5,060. The city is the site of a psychiatric hospital, Eastern State Hospital, and of Fairchild Air Force Base, two major employers.

The city of Medical Lake was incorporated in 1890. The city took its declare from the easy to use eponymous lake.

The Spokane people, a Native American tribe which had long inhabited the area, believed the water and mud of the lake to possess curative properties.

White settlers such as Andrew Lefevre and Stanley Hallett, who moved to the area in the 1870s, promoted this belief and marketed the lake salts for medicinal uses. A salt and soap industry developed here, followed by the construction of classified ad bath houses in the 1880s. This was a period taking into account springs and spas were popular developments across the country.

Several resort hotels were constructed along the lake shore. In 1891, the state build up Eastern State Hospital, and this additional stimulated economic growth in the city. Such buildup continued until the 1920s, when the lake declined in popularity as a tourist destination.