A central question in glioblastoma multiforme (GBM) research is the identity of the tumor-initiating cell, and its contribution to the malignant phenotype and genomic state. We examine the potential of adult lineage-restricted progenitors to induce fully penetrant GBM using CNS progenitor-specific inducible Cre mice to mutate Nf1, Trp53, and Pten. We identify two phenotypically and molecularly distinct GBM subtypes governed by identical driver mutations. We demonstrate that the two subtypes arise from functionally independent pools of adult CNS progenitors. Despite histologic identity as GBM, these tumor types are separable based on the lineage of the tumor-initiating cell. These studies point to the cell of origin as a major determinant of GBM subtype diversity. •Adult lineage-restricted CNS progenitors, like stem cells, can give rise to GBM•Two different GBM-initiating CNS progenitors are induced by identical mutations•Histologically and molecularly distinct GBMs arise from different CNS progenitors•The cell of origin emerges as a major determinant of GBM molecular subtype Alcantara Llaguno et al. examine the potential of adult CNS lineage-restricted progenitors to induce fully penetrant glioblastoma multiforme (GBM) and show that the same genetic drivers in different cells of origin generate molecularly distinct GBM subtypes.