And back problems and arthritis round out the top three, according to latest National Health Survey.
Mental and behavioural conditions have once again topped the National Health Survey in terms of prevalence, with one in five Australians dealing with a mental illness in 2020-21.
Up behind mental illness was back problems, affecting about 16% of the population and arthritis, affecting about 12%.
The survey, which is conducted by the Australian Bureau of Statistics every three years, was done completely online for the first time in 2020.
Data was collected from about 11,000 households around the country between August 2020 and June 2021.
Poor mental health affected more women than men and was more prevalent in people aged 15-34.
Women aged 15 to 24 had the highest rate of mental illness, at just over 30%, compared to the national average of 20%.
Anxiety and depression were the most commonly reported mental health conditions.
Unlike mental health issues, arthritis was most commonly reported by older age groups, ultimately affecting about 20% of people aged 75 or older.
Of the 10 chronic diseases measured by the ABS, kidney disease, cancer and COPD were three least common, all sitting between 1% and 1.5% of the population.
Even though the total number of people with COPD was small, at 1.5%, about 90% of people with COPD had another condition.
At the opposite end of the spectrum, people with mental health issues were the least likely cohort to have a comorbidity.
There was also a gender gap: only 44% of men, compared to 49% of women, reported having one or more conditions.
Men were, however, about twice as likely to have had a heart attack or cancer and had roughly the same incidence of kidney disease as women.
Outside of chronic disease, about a quarter of Australians are short-sighted, while one in five is long sighted. Around 20% of people experience hayfever and one in 10 has an allergy.
The survey also measures fruit and vegetable intake; alarmingly, only 6% of people regularly meet the recommended serving of fruit and vegetables each day.
While 41% of men and 49% of women do meet the recommended two or more servings of fruit per day, just 4% of men and 13% of women eat the recommended five to six serves of vegetables.
On a more reassuring note, the majority of respondents (60%) indicated that they did not usually drink sugar-sweetened beverages, the subject of a current AMA campaign.
