The National Inpatient Sample (NIS) is a database of hospital inpatient stays. It was developed by the Healthcare Cost and Utilization Project (HCUP), and up until 2011 was known as the Nationwide Inpatient Sample. The name and the design of the database changed in 2012. The NIS was formerly a sample of hospitals, with all discharges retained, but in 2012 the design changed to become a sample of discharges from all participating hospitals. Variables captured in the database include patient demographics, diagnosis and procedure codes, admission and discharge status, length of stay, expected payer, total charges, and hospital characteristics.

When the NIS began in 1988, eight states were included. As of 2012, data from 44 states were included in the NIS.