The malleus is the outermost and largest of the three small bones in the middle ear, and reaches an average length of about eight millimeters in the typical adult.

It is informally referred to as a hammer, owing to it being a hammer-shaped ossicle or small bone that is connected to the ear. It is composed of the head, neck, anterior process, lateral process, and manubrium.

When sound reaches the tympanic membrane (eardrum), the malleus transmits these sound vibrations from the eardrum to the incus, and then to the stapes, which is connected to the oval window. Because the malleus is directly connected to the eardrum, it is unlikely that it will be the cause of hearing loss.

In cases of atticoantral disease, an inflammatory disease of the middle ear, the ossicular chain (malleus, incus, and stapes) is often affected by abnormal skin growth, called cholesteatoma. This can cause loss of hearing. The malleus and or incus may have to be removed in order to remove all of the cholesteatomas. In cases like these, there may be a second surgery needed for reconstruction purposes.