Kniest dysplasia is a rare disease from the group of osteochondrodysplasias, rated type II colagenopathies, and like other skeletal dysplasias may be associated with defects of cranio-vertebral junction with atlanto-axial instability. Objects: a case of spontaneous atlantoaxial subluxation with spinal canal narrowing at the level of craniovertebral junction in twins with Kniest dysplasia was presented. Methods: on the basis of clinical examination, radiographs and MRI study, children were qualified for operative treatment - posterior widening of the foramen magnum and occipito-cervical fusion with titanium anchors. During control examination 4 years after primary surgery, patients was very active, without any neurological deficits, x-ray pictures and MRI study revealed widening of the foramen magnum and full fusion in the place of surgery. Conclusion: authors suggestion is that in the case of foramen magnum and spinal canal narrowing, operative treatment with decompression of nervous structures and stabilization should be advised.