Published descriptions of the biology of the spectacled porpoise, Australophocaena dioptrica, are reviewed and compared to new material collected in Tierra del Fuego and Chubut, Argentina. Although over 173 cranial and about 120 additional postcranial specimens have been found, minimal external measurements are available for only 28 individuals; 7 females, 11 males, 9 animals of unknown sex and 1 foetus. Males ranged in length from 109 to 224cm, females from 124.6 to 203.5cm. The smallest neonate (of unknown sex) measured 94cm, a foetus 48.4cm. Two females of 183 and 186cm were sexually mature; a female of 203.5cm was physically mature, a male of 224cm had just reached maturity. This probably does not represent the maximum size for the species. The maximum age to date («=27) was an animal of unknown sex with 8 GLGs. Two physically adult males had 4 and 5 GLGs, and one female had 6. Young animals (n=4) are dark grey dorsally and light grey ventrally with darker grey or brownish streaks, including a well-defined mouth to flipper stripe. This pigmentation changes in the adult to black on the dorsal surface, sharply separated from the pure white ventral region. The flipper stripe seems to lighten or disappear with growth. Both young and adults have variably shaped dark eye patches outlined in white and dark lips. Most animals had a dark upper tail stock and dark flukes and flippers, which are lighter below. A live stranding of a calf is described. The stranding distribution ranges from southern Brazil (32°S) to Tierra del Fuego (55°S) in the southwestern South Atlantic and to offshore islands of the Southern Ocean: South Georgia, Auckland, Macquarie and Heard. Spectacled porpoises have been sighted both inshore and far from the coast, off eastern South America, Kerguelen, south of Tasmania and south and southeast of New Zealand; the southernmost sighting was at 58°05’S in the Drake Passage. Two specimens and several sightings were near or south of the Antarctic Convergence. The porpoises may enter rivers and channels. Food habits are unknown, but one stomach contained meagre amounts of anchovy and stomatopods. In the southwestern South Atlantic, neonates and young calves stranded in February, March and May; birth is probably in late spring or summer (November to February). These porpoises are taken incidentally in nets; the amount of exploitation is unknown, but is probably higher than formerly thought. Nothing is known of the abundance, habitat preference, seasonal movements or behaviour of this species.