Adult fish can grow to in length, and in thickness. Adult males tend to be larger than females. Yellow tangs are bright yellow in color. At night, the yellow coloring fades slightly, and a prominent brownish patch develops in the middle with a horizontal white band. They rapidly regain their bright yellow color during daylight. They can be aggressive, are prone to marine ich, and may damage coral within a reef tank. Male and female yellow tang look very similar. When mating, however, males change color and have a "shimmering" behavior which makes them identifiable. The yellow tang has 5 dorsal spines along with 23–26 dorsal soft rays. The yellow tang also has 3 anal spines as well as 19–22 anal soft rays. There is a white spine on its caudal peduncle that it can use for defense. Its snout is moderately protruding. Its mouth is small with spatulate teeth that are place classed relatively close together inside of the yellow tang's mouth. In juveniles, there are 12 upper and 14 lower teeth. In adults, there are 18 upper and 22 lower teeth.
