Developed at the Duke University Medical Center of Durham, North Carolina, U.S.A., the Duke Severity of Illness Checklist (DUSOI) is a tool for measuring a person's illness severity. The instrument comprises four parameters of a health problem, e.g. in a given diagnosis, namely: symptoms, complications, 6-months prognosis without treatment, treatment potential. Using the numerical ratings (from 0 to 4) for each parameter of every diagnosis, the following three types of severity score (from 0 [lowest degree of severity] to 100 [highest degree of severity]) can be calculated: (1) the DUSOI diagnosis score for each diagnosis stated, (2) the DUSOI overall score for the set of all health problems stated for a patient, and (3) the DUSOI comorbidity score, i.e., all problems except for any one problem of principal interest. The DUSOI is suitable for patients from the entire chain of medical and rehabilitative care, although it had initially been developed for the ambulatory sector. Completing the DUSOI form is very economical in terms of time needed, and is recommended to be done by the physician in charge immediately following the patient's visit. Alternatively, the form could also be filled in by a reviewer on the basis of the patient's medical record. A certain level of judgement is required on the part of the physician or reviewer carrying out the DUSOI assessments.