It has been argued that mice should be housed at 30 °C to best mimic the thermal conditions experienced by humans, and that the current practice of housing mice at 20-22 °C impairs the suitability of mice as a model for human physiology and disease. In the current paper we challenge this notion. First, we show that humans routinely occupy environments about 3 °C below their lower critical temperature (T lc), which when lightly clothed is about 23 °C. Second, we review the data for the T lc of mice. Mouse T lc is dependent on body weight and about 26-28 °C for adult mice weighing >25 g. The equivalent temperature to that normally experienced by humans for most single housed adult mice is therefore 23-25 °C. Group housing or providing the mice with bedding and nesting material might lower this to about 20-22 °C, close to current standard practice.