Control of the stem-like tumour cell population is considered key to realizing the long-term survival of patients with glioblastoma, one of the most devastating human malignancies. To date, possible therapeutic targets and targeting methods have been described, but none has yet proven to target stem-like glioblastoma cells in the brain to the extent necessary to provide a survival benefit. Here we show that targeting JNK in vivo, the activity of which is required for the maintenance of stem-like glioblastoma cells, via transient, systemic administration of a small-molecule JNK inhibitor depletes the self-renewing and tumour-initiating populations within established tumours, inhibits tumour formation by stem-like glioblastoma cells in the brain, and provide substantial survival benefit without evidence of adverse events. Our findings not only implicate JNK in the maintenance of stem-like glioblastoma cells but also demonstrate that JNK is a viable, clinically relevant therapeutic target in the control of stem-like glioblastoma cells.