PURPOSE: To delineate the nature of the capsule of the nerve to the inferior oblique muscle along its intra- and extracranial course and to compare it to the capsules of the nerves to the other extraocular muscles; also to determine any change in the nature of the capsule from birth to adulthood. METHODS: Light and electron microscopy were performed on fresh autopsy specimens from a neonatal and a 26-year-old cadaver. RESULTS: The collagenous capsule of the nerve to the inferior oblique is present throughout its entire course, becoming more complex anteriorly as the myoneural junction is approached. A similar capsule surrounds the nerves to the other extraocular muscles. This structure is well developed by birth. CONCLUSIONS: The mechanical inelasticity of the nerve to the inferior oblique muscle has been shown to influence postoperative ocular alignment. The nerve is surrounded by a collagenous and fibrous capsule, which is well developed along the entire course of the nerve and is present from birth. The nerves to the other extraocular muscles have a similar capsule that likely conveys similar mechanical properties to those nerves and that may affect ocular alignment following surgical procedures on these muscles as well. These findings expand our current understanding of the nerves to the extraocular muscles and may be useful for improving treatments.