Observer-based estimates of the quantities and size compositions of discarded and retained catches from the commercial beach-seine fishery in Botany Bay, NSW, Australia are presented. A total of 71 finfish and 10 invertebrate taxa were identified in catches sampled between February 1998 and February 1999, with 39 taxa being retained by fishers and 77 taxa discarded. Gerres subfasciatus, Pseudocaranx dentex, Sillago ciliata, Acanthopagrus australis and Rhabdosargus sarba dominated retained catches. Discards included small individuals of many retained species that are also important in other commercial and recreational fisheries, including S. ciliata, A. australis, R. sarba, Pagrus auratus, Meuschenia freycineti and Scobinichthys granulatus, as well as some non-monetary valued species such as Dicotylichthys punctulatus, Anoplocapros inermis and several tetraodontids. The estimated monthly ratio of retained to discarded catch (kg) ranged from 1:0.26 to 1:2.48. An estimated 44% of total individuals and 38% of the total weight of catches were discarded. It was estimated that this fishery annually discarded 93 t of fish and invertebrates, which included hundreds of, thousands of commercially and recreationally important species. The results are discussed in terms of their consequences for interactions with other fisheries.