A detailed study of a territorial form of the striped parrotfish (Scarus croicensis) was done on the reefs surrounding Isla Pico Feo on the Caribbean coast of Panama. Territories were located in shallow water (less than 3 m), averaged 12 m2 in size, and appeared to serve as feeding and occasionally spawning grounds. The dominant territorial fish was female. A terminal—phase male, which may be paired with the female, usually defended the same area. Uncommonly a striped—phased male defended the territory in place of or in addition to the terminal—phase male. The territorial female tolerated the presence of one to three subordinate non—territorial females. These associations of territorial fish remained constant for varying periods of time, and if a fish was removed, either naturally or experimentally, it would be rapidly replaced. The characteristic territorial display by the female involved the extension of yellow pelvic fins. Highly aggressive displays between neighboring territorial females involved mouth—to—mouth interactions. All territorial behavior was directed intraspecifically, but extensive interspecific interactions were also observed. Interaction between the territorial female and the territorial male varied with spawning condition. Territorial behavior in striped parrotfish may be related to proterogynous sex reversal in the scarids.