Longlining operations for Dissostichus eleginoides around South Georgia were assessed for interactions with sea mammals. Twenty-seven lines were observed and interactions recorded during twenty-five of these. During setting of lines neither mortalities nor interactions were recorded. All interactions occured during hauling operations, both during the day and at night. Killer whales (Orcinus orca)were present during one haul, from which 11 intact fish were taken aboard, compared to a mean of 510 fish/haul for all 27 lines. Sperm whales (Physeter macrocephalus) were also associated with hauling operations and may have been removing fish captured on the lines. Numbers of sperm whales varied with location; some whales with identifying masks were observed over successive lines to the south-west of South Georgia, but were not seen on subsequent operations to the north-west of the island. On two occasions, sperm whales were snagged on the line but were freed. Interviews with fishermen indicated that interactions of killer whales and sperm whales with longlining operations may be common in the South Atlantic and off southern Chile. Fishermen recognized that these interactions were costly in terms of fish and fishing time lost; the development of measures to reduce interactions may help prevent fishermen taking action potentially harmful to cetaceans.