Sooty Tern, Onychoprion fuscatus (Linnaeus 1766), is a rare species along the Brazilian coast due to oceanic habits. We report the first documented record of this species from São Paulo state, southeastern Brazil. The specimen was found beached in Mongaguá municipality. Morphological assessment, necropsy, and histological analysis allowed us to identify species, reproductive state (non-breeding), and sex (male) of this specimen.