ObjectiveTo clarify the characteristics and clinical signiifcance of the NOTCH1 mutations in childhood T-cell acute lymphoblastic leukemia (T-ALL).MethodsAmplify and sequence the heterodimerization (HD) domain and the pro-line-glutamicacid-serine-threonine (PEST) domain of theNOTCH1 gene in 28 T-ALL children, in order to explore the frequency, position and type of the mutations as well as their reletions with prognosis.ResultsIn 28 children with T-ALL, 15 cases (51.57%) had been identiifed theNOTCH1 mutations, all of which were heterozygous mutations. The lymphoblast counts in peripher-al blood and bone marrow in theNOTCH1 mutant group at admission were signiifcantly higher than in the non-mutant group (P<0.05). The 1-year remission rate in the 28 children with T-ALL was 75% (21/28), including 80% (12/15) in mutant group in which 3 patients relapsed and all of them died (1-year mortality 20%) and 69.20% (9/13) in non-mutant group in which 4 patients relapsed but all survived (1-year mortality 0%).ConclusionsThe children with T-ALL had a high incidence of NOTCH1 mu-tations at various sites. In addition, the patients withNOTCH1 mutations had more severe disease at diagnosis, better short-term prognosis and poor outcome with salvage therapy after relapse.