This study describes marked differences in the antitumour immune response among mice housed at different temperatures. Healthy mice prefer an ambient temperature of 30–31 °C (known as 'thermoneutrality'), but the standard housing temperature for laboratory mice is 20–26 °C (known as 'subthermoneutrality'), which causes chronic metabolic cold stress. In several mouse tumour models (of transplanted and chemically induced tumours), tumour growth and metastasis were increased in wild-type, but not in immunodeficient, mice that were housed at subthermoneutrality compared with those housed at thermoneutrality. Activated, antigen-specific CD8+ T cells were present at a higher frequency in mice housed in thermoneutral environments and were required for the delay in tumour growth. Also, tumour-bearing mice housed at thermoneutrality had fewer immunosuppressive cells — regulatory T cells and myeloid-derived suppressor cells — than mice housed at subthermoneutrality. Furthermore, tumour-bearing mice preferred a temperature of 38 °C; the authors suggest that the metabolic stress of tumour growth may compound the effects of cold stress on the immune system.