Dilophosaurus was named "two-crested lizard" or "two ridged reptile" due to its pair of large, extensive but paper thin crests that projected from the top of the skull behind and running between the eyes down to the top of its nostrils or snout. Other theropods had crests, such as its contemporary Syntarsus, but none were as prominent as dilophsaurus. There was a thin bone in each crest with shallow pits or holes that may have served as air sacs in what appears to be very delicate structures. The pits are more apparent in the Chinese variety, but clearly noticeable in the US specimens. It is suggested the crests were used as a signaling device such as a warning display or for social position. They may also have been a distinguishing feature between male and female or between species. The crests at least made the head look more round and larger than it otherwise would have been without them.

The front teeth were long and slender. The cheek-teeth were long, pointed, and blade-shaped. The lower jaw was slender and some scientists have suggested it was not strong enough to have fed on live prey but rather clawed to kill and then fed on the carcasses or may have scavenged animal carcasses killed by other predators. It was nevertheless the dominant predator of its time and fed on the large plant-eating prosauropod dinosaurs and other prey.

Three of the four fingers on the "hands" had claws. The rear legs were long