This paper adds a new type of association between cetaceans and seabirds during fishing events, not yet reported in the literature: kleptoparasitism between frigatebirds, Fregata magnificens, and harbor porpoises, Sotalia fluviatilis, in the Paraty Bay region (23°56'S; 44°19'W), south of the state of Rio de Janeiro, southeastern Brazil. Between April 1997 and January 1999, 21 cruises were carried out to study the distribution, movements and behavior of cetaceans in Paraty Bay.