They generally look like a child of about ten years or so, usually a bald-headed young Buddhist monk, but its face is dominated by its one huge eye. They are often shown with a long tongue, wearing a straw hat that might hide it's strange features, and a lantern (like most ghost-typed Yōkai, they appear mostly at night).
Like many obake who are largely human in appearance, the Hitotsume-kozō enjoys using its monstrous attributes to surprise and frighten people, and loves sassing the humans it meets, telling them to "be quiet!" (they like the silence) or greeting them with other childish chides and mockery.
Sometimes said to be spirits of disease that appear on the eighth of the month, the one-eyed boys can be
repelled by hanging baskets in doorways ; the cycloptic little monsters see the basket's many holes as a vast amount of eyes, and run away in jealousy, ashamed of only having one.
In reality, apart from a few tricks, they are almost never known to intentionally cause harm to anyone and may even bring good fortune.