Glioblastoma tumors (GBM) are very heterogeneous, being comprised of several cell subtypes, including glioblastoma stem cells (GSC). These tumors have a high rate of recurrence after initial treatment and one of the most prevalent theories to explain this is the cancer stem cell theory, which proposes that glioblastomas arise from mutations that transform normal neural stem cells (NSC) into GSC, which are highly resistant to oxidative stress and anti-cancer therapies. Sulindac is a non-steroidal anti-inflammatory drug (NSAID) that has been shown to protect the normal cells against oxidative damage by initiating a preconditioning response, but selectively sensitizes several cancer cell lines to agents that affect mitochondrial respiration, resulting in enhanced killing of the cancer cells. These effects of sulindac are independent of its NSAID activity. There is little information on the effect of sulindac on normal and cancer stem cells. To study the effect of sulindac on both normal and cancer stem cells, we have isolated normal neural stem cells (NSC), from mice hippocampi and glioblastoma stem cells (GSC) from a glioma cell line, U87. As expected from previous studies sulindac can protect normal astrocytes against oxidative stress. Sulindac induces differentiation of both NSC and GSC cells and sulindac upregulates neurogenesis in NSC. The differentiated NSC are also protected from oxidative stress damage, whereas the differentiation of GSC by sulindac increases the sensitivity of these cells to agents that cause oxidative stress. The S epimer of sulindac is more effective than the R epimer in inducing neuronal differentiation in both NSC and GSC. These results indicate that the ability of sulindac to induce GSC differentiation may have therapeutic value in preventing tumour recurrence.