The main pattern of this species is dark above, light below, with a tendency for the dorsal fin to darken considerably in adults. In the young the belly is cream which darkens to a blue-grey hide. There is an eye patch which is also dark, with females alone developing both white upper and lower jaws and scars. The lower jaw is arched in the same fashion as the Right Whales', with a prominent tooth erupting at the peak of this arch in males. The maximum recorded lengths have been 4.7 m in both males and female (Ward 2001).

The male Blainville's Beaked Whale is one of the oddest-looking of all cetaceans. It has a pair of massive teeth that grow from substantial bulges in its lower jaw, like a couple of horns; these may be so encrusted with barnacles that the animal appears to have 2 dark-coloured pompons on top of its head. This feature makes it relatively easy to identify at sea, although it is generally inconspicuous and difficult to find; it is known mainly from strandings. The flattened forehead and large spots all over its body, possibly made by the teeth of Cookie-cutter Sharks and parasites, are also characteristic.