About one in five Australians will experience a mental illness each year, and most of us will experience a mental health problem at some time or another in our lives.
Mental illness is a general term that refers to a group of illnesses, in the same way that heart disease refers to a group of illnesses and disorders affecting the heart.
A mental illness is a health problem that significantly affects how a person feels, thinks, behaves, and interacts with other people. It is diagnosed according to standardised criteria. The term mental disorder is also used to refer to these health problems.
A mental health problem also interferes with how a person thinks, feels, and behaves, but to a lesser extent than a mental illness.
Source: What is mental illness? Mental Health and Workforce Division of the Australian Government Department of Health and Ageing (2007)