Cleavage of the gasdermin proteins to produce pore-forming amino-terminal fragments causes inflammatory cell death (pyroptosis)(1). Gasdermin E (GSDME, also known as DFNA5)-mutated in familial ageing-related hearing loss(2)-can be cleaved by caspase 3, thereby converting noninflammatory apoptosis to pyroptosis in GSDME-expressing cells(3-5). GSDME expression is suppressed in many cancers, and reduced GSDME levels are associated with decreased survival as a result of breast cancer(2,6), suggesting that GSDME might be a tumour suppressor. Here we show that 20 of 22 tested cancer-associated GSDME mutations reduce GSDME function. In mice, knocking out Gsdme in GSDME-expressing tumours enhances, whereas ectopic expression in Gsdme-repressed tumours inhibits, tumour growth. This tumour suppression is mediated by killer cytotoxic lymphocytes: it is abrogated in perforin-deficient mice or mice depleted of killer lymphocytes. GSDME expression enhances the phagocytosis of tumour cells by tumour-associated macrophages, as well as the number and functions of tumour-infiltrating natural-killer and CD8(+) T lymphocytes. Killer-cell granzyme B also activates caspase-independent pyroptosis in target cells by directly cleaving GSDME at the same site as caspase 3. Uncleavable or pore-defective GSDME proteins are not tumour suppressive. Thus, tumour GSDME acts as a tumour suppressor by activating pyroptosis, enhancing anti-tumour immunity. The gasdermin E protein is shown to act as a tumour suppressor: it is cleaved by caspase 3 and granzyme B and leads to pyroptosis of cancer cells, provoking an immune response to the tumour.