A classification of a hospital stay in terms of what was wrong with and what was done for a patient. The DRG classification (one of about 500) is determined by a "grouper" program based on diagnoses and procedures coded in ICD-9-CM, and on patient age, sex, length of stay, and other factors. The DRG frequently determines the amount of money that will be reimbursed, independently of the charges that the hospital may have incurred.