This paper investigates the relationship between temperature and hospitalization in China. Using inpatient visit claims of two major public insurance schemes covering 47 cities in 28 provinces for three years, we see a 7.3% increase in hospital admissions on days on which the average temperature is above 27 degrees C, and a 2% increase in 31-day cumulative hospital admissions relative to a benchmark-temperature day in the subsequent weeks. Such an effect is much larger than evidence from developed economies. Using detailed information on medical bills, we calculate that an additional hot day nationwide is associated with approximately 2 billion yuan (roughly equivalent to 0.3 billion US dollars) increase in medical expenses that are related to inpatient services, 1.9 billion yuan (roughly equivalent to 0.29 billion US dollars) of which is borne by the public insurance system, and 0.2 billion yuan (roughly equivalent to 0.01 billion US dollars) of which is borne by the insured.