The virtually hairless hide ranges from grey to brown in colour, with the underparts lighter. This light colour may extend onto the lips. The hide often has large folds near the neck and belly, and the sparsely distributed hairs are yellowish. The babirusa has a rounded body, supported by relatively long, thin legs. In males, the upper tusks protrude upwards through the snout and arc backwards, to a maximum length of 31 cm / 12.4 inches. These canines are mobile in their sockets, and break easily. The lower ones protrude from the sides of the mouth, and along with the gruesome upper tusks, give the babirusa a formidable appearance.
The female nurses the young lying down, and despite the lengthy nursing period, they may begin to eat solid food only 3-10 days after birth.
The babirusa is primarily diurnal, with a tendency to feed in the morning. Well worn paths through the jungle are used by these pigs when travelling. The babirusa is a swift runner as well as a good swimmer, and has even been recorded swimming to off-shore islands. Mud wallowing is a frequently recorded activity, while rooting with the snout - an action commonly seen in other pigs - is very uncommon. Captive individuals have been noted making nests of straw to rest in. Males must sharpen their lower tusks by rubbing them on trees, since they do not self-sharpen against the upper canines as in other pigs. These lower canines are used in an offensive manner, while the curled upper tusks probably act as a defensive shield. These long teeth are fairly brittle and are easily broken off. The senses of smell and hearing are well developed. The main vocalization is a low grunt or moan, and, when excited, they clatter their teeth.
While its general form is pig-like, the babirusa's peculiarities have warranted the creation of a separate genus. Recent studies of fossils show that this species may be more closely related to hippopotamuses than pigs, although how this fits in with the recent hippopotamus-cetacean relationship is unknown. Native legend has it that at night the babirusa hangs with its tusks from the branch of a tree. The hooked tusks are also said to look like (and have the same general function as) antlers, which is reflected in the name "babirusa", which means "pig-deer".