Adults are reef fish, often solitary and territorial, and live around sand or rubble bottom up to a depth of 50 m (160 ft).

[4] The longhorn cowfish was first formally described as Ostracion cornutus in the 10th edition of Systema Naturae published in 1758 by Carl Linnaeus with its type locality given as India.

[5] In 1902 David Starr Jordan and Henry Weed Fowler proposed the subgenus Lactoria within Ostracion and designated O. cornutus as its type species.

[6] The 5th edition of Fishes of the World classifies this genus within the family Ostraciidae in the suborder Ostracioidea within the order Tetraodontiformes.

[7] The longhorn cowfish is classified within the genus Lactoria, a name that means a "milkcow", a reference to the large spines above the eyes resembling the horns of a cow.

The specimens found in India are a new development in the last couple years, and it is speculated that cyclones or typhoons brought Lactoria cornuta to a new environment.

[10][11] There is no known sexual dimorphism, so both male and female display a yellow to olive base color, which is decorated with white or bluish spots.

The hexagonal plate-like scales of these fish are fused together into a solid, triangular, box-like carapace, from which the fins and tail protrude.

If severely stressed, this species may be able to exude deadly toxin, pahutoxin, an ichthyotoxic, hemolytic, heat-stable, non-dialyzable, non-protein poison in the mucous secretions of their skin.

It is apparently unique among known fish poisons; it is toxic to the boxfish and mimics sea cucumber toxins in general properties.