Additional diagnosis must be in accordance with the ICD-10-AM Australian Coding Standards. Generally, external cause, place of occurrence and activity codes will be included in the string of additional diagnosis codes. In some data collections these codes may also be copied into specific fields.

The diagnosis can include a disease, condition, injury, poisoning, sign, symptom, abnormal finding, complaint, or other factor influencing health status.

Additional diagnoses give information on the conditions that are significant in terms of treatment required, investigations needed and resources used during the episode of care.