The ability to prospectively isolate adult neural stem cells and their progeny is crucial to study their biology and therapeutic potential. Stem cells in adult mammalian neurogenic niches are a subset of astrocytes. A major limitation in the field has been the inability to distinguish stem cell astrocytes from niche astrocytes. Here, we show that epidermal growth factor receptor (EGFR)-positive subventricular-zone (SVZ) astrocytes are activated stem cells that are eliminated by antimitotic treatment. We developed a simple strategy to simultaneously purify cells at different stages of the adult SVZ stem cell lineage by using FACS. This method combines the use of fluorescent EGF ligand, CD24, and GFP expression in GFAP::GFP transgenic mice and allows the simultaneous purification of activated stem cell astrocytes (GFP⁺EGFR⁺CD24⁻), niche astrocytes (GFP⁺EGFR⁻CD24⁻), transit amplifying cells (GFP⁻EGFR⁺CD24⁻), and neuroblasts (GFP⁻EGFR⁻CD24^low). One in three EGFR⁺ astrocytes gives rise to neurospheres in vitro, a 20-fold enrichment over unsorted cells. Importantly, these cells constitute the neurosphere-forming population among SVZ astrocytes. This approach will be of great utility for future functional and molecular studies of the SVZ stem cell lineage.