Background: It is generally recommended that conservative treatment for atlanto-axial subluxation (AARS) is abandoned, in favour of surgical spondylodesis, 3 months after an incident leading to the condition. However, where bony deformation has occurred and this is in a growing individual, bony re-modelling is known to take place and a chance of normalizing bony deformation and consequently of correcting head position and movement still exists. The purpose of this study is to present a hitherto undescribed bony deformation as a possible background for persistent AARS and to illustrate the re-modelling of the deformation through conservative treatment. Patient and methods: The patient was treated in the in-patient clinic for 14 days with Gartner traction and manual therapy, then with out-patient treatment for 16 weeks. For the first 8 weeks, she wore a rigid cervical orthosis constantly and also had manual therapy 3 times weekly. During the following 8 weeks, the orthosis was slowly exchanged for a soft collar, the use of which was reduced through the period and then stopped. In the same period, the frequency of manual treatment was likewise gradually reduced in favour of home exercises. A single Botox (botunlinum toxin) injection was given approximately half-way through the out-patient treatment period. Results: During the out-patient period, active cervical rotation to the right was increased from 45° to 70°, and extension from 15° to 90°. At 1-year follow-up, active cervical movements were: rotation right/left: 65°/80°, extension: 90°, and control MRI-scan indicated normalisation of the bony deformation. Conclusions: The clinical result shows that conservative treatment can still be effective even after 6 months' persistence of the Cock-Robin position. Furthermore, the results of the CT- and MRI-scans indicate that re-modelling of a bony deformation of the lateral mass of C2 occurs even 6 months after an incident leading to AARS. Further studies are needed in order to make a general recommendation of this treatment in long-lasting cases of AARS before surgery is considered.