Fifteen patients with atlanto-axial instability (secondary to os odontoideum in three, nonunion of an odontoid fracture in seven, acute odontoid fracture in three, and rheumatoid arthirtis in two) were treated by wedge compression arthrodesis of the atlanto-axial joint. One patient died at home eight weeks after fusion with the cause of death never established. Of the two patients with rheumatoid arthritis (ankylosing spondylitis), one had a non-union and in the other the posterior arch of the atlas fractured and the fusion had to be extended up to the occiput and down to the third cervical vertebra. The procedure is rarely indicated in patients with long-standing rheumatoid arthritis or severe osteopenia.