Somatic mutations in the catalytic domain of isocitrate dehydrogenase (IDH) 1/2 and accumulation of the oncometabolite 2-hydroxyglutarate (2-HG) appear to be among the earliest events in gliomagenesis and may contribute to malignant transformation. The lack of cell lines with endogenous mutations has been one of the major challenges in studying IDH1/2-mutant glioma and developing novel therapeutics for these tumors. Here, we describe the isolation of a glioma brain tumor stem cell line (BT142) with an endogenous R132H mutation in IDH1, aggressive tumor-initiating capacity, and 2-HG production. The neurosphere culture method was used to establish a brain tumor stem cell line from an IDH1-mutant anaplastic oligoastrocytoma sample, and an orthotopic xenograft system was developed to allow its rapid expansion. Production of 2-HG by glioma cells with endogenous IDH1 mutations was confirmed by mass spectrometry. BT142 retained an endogenous R132H IDH1 mutation in culture and possessed aggressive tumor-initiating capacity, allowing it to be readily propagated in orthotopic xenografts of nonobese diabetic/severe combined immune deficiency (NOD SCID) mice. Endogenous 2-HG production by BT142 was detectable in both cell culture medium and xenograft animal serum. BT142 is the first brain tumor cell line with an endogenous IDH1 mutation and detectable 2-HG production both in vitro and in vivo, which thus provides a unique model for studying the biology of IDH1-mutant glioma and in vivo validation of compounds targeting IDH1-mutant cells.