Hemi-atlas is a rare congenital anomaly in the formation of the first cervical vertebra. It may cause a rather severe and progressive torticollis. When a child is young, the neck, despite the deformity, is flexible and the torticollis can be passively corrected. However, in some patients it becomes increasingly severe and fixed. I describe the findings in seventeen patients, seven of whom were operated on between 1975 and 1983. Treatment with a brace was shown to be ineffective. In patients with severe deformities, fusion of the upper part of the cervical spine is recommended. Fusion was obtained in all seven patients in whom it was attempted, and there was good postural correction in all. Early operation is recommended if the deformity is increasing. Gradual correction in a halo cast followed by posterior fusion is recommended as the treatment of choice in patients with severe torticollis.