SUMMARY BACKGROUND Symptomatic Chiari Type I Malformation (CM) is treated with posterior fossa decompression with or without duroplasty. We have noticed some cases with concomitant severe cerebellar ataxia due to cerebellar atrophy. The aim of this study is to review the literature of CM associated with severe cerebellar atrophy and discuss its potential physiopathology. METHODS A systematic literature review in the Pubmed Database was performed using the following key-terms: "cerebellar atrophy Chiari", and "cerebellar degeneration Chiari". Articles reporting the presence of cerebellar degeneration/atrophy associated with CM were included. RESULTS We found only six studies directly discussing the association of cerebellar atrophy with CM, with a total of seven cases. We added one case of our own practice for additional discussion. Only speculative causes were described to justify cerebellar atrophy. The potential causes of cerebellar atrophy were diffuse cerebellar ischemia from chronic compression of small vessels (the most mentioned speculative cause), chronic raised intracranial pressure due to CSF block, chronic venous hypertension, and association with platybasia with ventral compression of the brainstem resulting in injury of the inferior olivary nuclei leading to mutual trophic effects in the cerebellum. Additionally, it is not impossible to rule out a degenerative cause for cerebellar atrophy without a causative reason. CONCLUSIONS Severe cerebellar atrophy is found in some patients with CM. Although chronic ischemia due to compression is the most presumed cause, other etiologies were proposed. The real reasons for cerebellar degeneration are not known. Further studies are necessary.