Hyperoodon planifrons individuals grow to about 8 meters in length. Sexual dimorphism is seen in this species, with the males averaging a length of 7.5 meters and the females averaging only 6.5 meters. Body mass has been estimated at 6 to 8 tons. The body of H. planifrons is cylindrical in shape and tapers toward the tail in the last 1/3 of its length. The tail flukes are wide and lack the notched center that is often seen in other cetaceans. Southern bottlenose whales have short, distinct beaks protruding from an inflated forehead or melon. In females and young males, the forehead slopes smoothly into the beak. In older males, the forehead rises abruptly from the beak. The dorsal fin of H. planifrons is located 2/3 of the body length from the head, measures between 30 to 40 cm, and is sickle-shaped with a blunt tip. This whale's flippers are small, short, and also blunt-tipped.

Male H. planifrons have one pair of short, conical teeth which are situated at the tip of the lower jaw. Teeth are not found in the upper jaw. The teeth of females are either smaller or do not emerge at all. Rows of vestigial teeth are often present in the lower and upper jaw.

Southern bottlenose whales are a brownish-grey color on the head, back, dorsal fin, flippers, and tail . This color is paler on the belly, throat, and sides. However, coloration becomes lighter with age. Calves are a grayish-brown to black color, while older whales are completely yellowish-white in color.

(Tinker 1988, Nowak 1997, Baker 1983, Minasian et al. 1984)