Filet-O-Fish is the McDonald’s product name for the fish sandwich introduced nationally in 1965.
McDonald’s franchisee Lou Groen developed the sandwich in Cincinnati, Ohio, where many customers observed meatless eating on Fridays. The original sandwich used a fried fish fillet, cheese, and tartar sauce on a bun. Its menu identity gave McDonald’s a recognizable seafood option alongside its hamburger products.
The sandwich was tested before receiving a national rollout in 1965. Its name combined a fish reference with McDonald’s familiar product naming style, helping it function as both a menu description and a branded item.
The Filet-O-Fish is sometimes confused with later limited-time seafood products. Those items came and went, while Filet-O-Fish remained one of McDonald’s long-running signature menu names.