A condition or complaint either coexisting with the principal diagnosis or arising during the episode of care or attendance at a health care facility.

Additional diagnoses should be interpreted as  additional conditions that affect patient care in terms of requiring any of the following:

- Therapeutic treatment
-Diagnostic procedures
- Increased nursing care and or monitoring

Additional diagnoses give information on factors which result in increased length of stay, more intensive treatment or the use of greater resources. They are required for casemix analyses relating to the severity of illness and for correct classification of patients into Australian National Diagnosis Related Groups.