Most common diagnoses

The principal diagnosis is the diagnosis established after study (for example, at the completion of the episode of care) to be chiefly responsible for causing the episode of admitted patient care. It is essentially the main reason a person needed to be admitted to hospital.

Diagnoses and related information (for example, external causes of injury) are recorded using the relevant version of the International statistical classification of diseases and related health problems, Australian modification (ICD-10-AM).

This section presents information on the numbers of hospitalisations by ICD-10-AM chapter, and the 20 most common detailed principal diagnoses (at the 3-character level) for public and private hospitals for 2024–25.

Most common principal diagnoses

In 2024–25:

• 1 in 4 (25%, 3.1 million) hospitalisations had a principal diagnosis of Factors influencing health status and contact with health services – which includes Care involving dialysis (around 1.8 million separations), radiotherapy and chemotherapy.
• The profile of principal diagnoses of patients tended to differ across public and private hospitals. For example, 87% of hospitalisations for Certain conditions originating in the perinatal period and 84% of hospitalisations for Certain infectious and parasitic diseases occurred in public hospitals, while private hospitals accounted for 72% of hospitalisations for Diseases of the eye and adnexa, and 69% of Diseases of the musculoskeletal system and connective tissue.
• 43% of hospitalisations for First Nations people had a principal diagnosis of Factors influencing health status and contact with health services – compared with almost 1 in 4 (24%) other Australians. (For more information relating to hospitalisations for First Nations people see the Aboriginal and Torres Strait Islander Health Performance Framework).

Same-day acute hospitalisations

In 2024–25:

• over half of all same-day acute hospitalisations were provided in public hospitals (4.3 million or 56%)
• nearly 1 in 4 (23%, 1.8 million) hospitalisations in both public and private hospitals were for Care involving dialysis, and 1 in 3 (33%) hospitalisations in public hospitals were for this diagnosis
• the majority of hospitalisations for Pain in throat and chest (92%) and Care involving dialysis (80%) took place in public hospitals
• the majority of hospitalisations for Procreative management (95%), Embedded and impacted teeth (94%), Other retinal disorders (87%), and Benign neoplasm of colon, rectum, anus and anal canal (80%) took place in private hospitals (private free-standing day facilities or other private hospitals).

Overnight acute hospitalisations

In 2024–25:

• 7 in 10 overnight acute hospitalisations were provided in public hospitals (3.0 million or 72%)
• the 2 most common principal diagnoses reported were Single delivery by caesarean section (which accounted for 2.7% of separations in both public and private hospitals) and Single spontaneous delivery (which accounted for 3.0% of separations in public hospitals and 1.5% in private hospitals)
• public hospitals provided a majority of hospitalisations for Other chronic obstructive pulmonary disease (91%), Acute appendicitis (87%), and Cellulitis (86%)
• private hospitals provided a majority of hospitalisations for Gonarthrosis (arthrosis of the knee, 73%), Coxarthrosis (arthrosis of hip, 72%) and Chronic ischaemic heart disease (62%).

Changes over time

Over the last five years, from 2020–21 to 2024–25:

• overnight acute hospitalisations with the principal diagnosis Other chronic obstructive pulmonary disease increased by 30%, from 45,400 to 58,800 separations
• overnight acute hospitalisations with the principal diagnosis Pneumonia, organism unspecified increased by 25%, from 43,600 to 54,500 separations
• overnight acute hospitalisations with the principal diagnosis Pain in throat and chest decreased by 25%, from 57,100 to 42,900 separations
• overnight acute hospitalisations with the principal diagnosis Abdominal and pelvic pain decreased by 12%, from 53,200 to 46,800 separations.