McDonald's introduced the Filet-O-Fish nationally in the United States in 1965.
The sandwich was created by McDonald's franchisee Lou Groen in Cincinnati, Ohio, where many customers observed Catholic dietary restrictions involving meat on Fridays. Groen developed a fish sandwich as a way to broaden the restaurant’s appeal during a period when Friday sales were weak.
The Filet-O-Fish became a durable part of McDonald's product branding through its distinctive name, fish-shaped imagery in promotions, and association with seasonal demand. Its continued presence also made it one of the chain’s best-known non-beef menu items.
The sandwich’s origin is often simplified into a generic “seafood option” story. The more specific background is that a franchisee developed it for a Cincinnati market and that McDonald's launched it nationally in 1965.