Five species of digeneans (4 Microphallidae, 1 Echinostomatidae) were recovered from a total of 85 Olrog's gulls, Larus atlanticus (dead chicks). Birds were collected from a breeding colony in the Bahía Blanca estuary, Argentina, during breeding seasons 2003 (n = 6), 2005 (n = 66), and 2006 (n = 13). Digeneans were identified as Maritrema bonaerensis, Maritrema orensensis, Odhneria odhneri, Levinseniella cruzi, and Himasthla escamosa. Except for M. bonaerensis, all other helminth species represent new host records, and all the digeneans reported constitute new locality records. Likely intermediate hosts for digeneans, such as Neohelice granulata (Crustacea: Decapoda), Cyrtograpsus angulatus (Crustacea: Decapoda), and Heleobia australis (Mollusca: Gastropoda), were also studied. The metacercariae of M. bonaerensis were found in the crabs N. granulata and C. angulatus, and cercariae closely resembling those of M. bonaerensis, L. cruzi and H. escamosa were found in the mollusc H. australis.