Marie et al. (1922) first proposed a disease entity "late cortical cerebellar atrophy (LCCA)", which is characterized neuropathologically by pure cerebello-olivary degeneration. LCCA was originally described as sporadic, late-onset, pure cerebellar ataxia of unknown etiology; however, it has occasionally been used to denote familial or secondary ataxias, particularly alcoholic cerebellar degeneration. Sporadic ataxia is classified mainly into LCCA or CCA and olivo-ponto-cerebellar atrophy (OPCA) in Japan. OPCA, now multiple system atrophy with predominant cerebellar ataxia, has characteristic brain imaging features and is clearly diagnosed based on the consensus criteria. On the other hand, there is no specific biomarker for LCCA/CCA, and neuropathological examination is required for a definitive diagnosis. Therefore, the clinical diagnosis of LCCA/CCA depends on the exclusion of other diseases manifesting as cerebellar ataxia. However the differential diagnosis for LCCA/CCA is not necessarily made carefully. As a result, the LCCA/CCA category in Japan is a "waste basket," including OPCA, hereditary ataxias, and secondary ataxias, which are unidentified yet. To refine the LCCA/CCA category, we proposed the clinically-defined term "idiopathic cerebellar ataxia (IDCA)" and established its diagnostic criteria. By nationwide screening, we have identified 51 patients with probable IDCA according to the criteria so far. Here we review the clinical characteristics of IDCA patients.