(Very) severe acquired aplastic anemia ((v)SAA) and myelodysplastic syndrome (MDS) are rare diseases in childhood. (V)SAA is a bone marrow (BM) failure syndrome characterized by immune-mediated destruction of hematopoietic progenitors. MDS is a malignant clonal stem cell disorder, of which the hypoplastic variant is, in case of absence of a cytogenetic clone, difficult to separate from (v)SAA. Recently, studies provided a molecular signature of autoimmunity in adult (v)SAA, by showing oligoclonality based on the length of the TCR Vbeta CDR3 region. We investigated retrospectively the frequency and the discriminative value of TCR Vbeta CDR3 oligoclonality in pediatric (v)SAA and MDS patients. Peripheral blood (PB) and/or BM mononuclear cell samples of pediatric patients with (v)SAA (n=38), refractory cytopenia (MDS-RC) (n=28) and 18 controls were analysed via TCR Vbeta heteroduplex PCR analysis of extracted RNA. A skewed TCR Vbeta CDR3 repertoire was found in 21/38 (v)SAA and in 17/28 RC patients in contrast to 2/18 in the control group. These data suggest an overlapping group of RC and SAA patients that may share a common immune-mediated pathogenesis. Prospective studies are required to establish the clinical value of TCR Vbeta CDR3 repertoire analysis to predict the clinical response in these patients.