Severe idiopathic cytopenia(initially neutropenia)of undetermined significance(ICUS)was identified in an elderly patient. Immature blasts and dysplastic cells were not observed, and the karyotypic analysis was normal. These hematological findings did not meet the minimal diagnostic criteria for myelodysplastic syndrome(MDS). Causative disease and drugs were excluded. Cases of ICUS that have the possibility of evolving into MDS are expected to increase in the elderly.