Prader-Willi Syndrome is a rare and complex genetic condition, affecting roughly 400,000 people worldwide (or 1:15,000 worldwide).

Information on the prevalence of people with PWS is limited.

The number of people in Australia with known PWS by year of birth, based on data from the Australian Prader-Willi syndrome database, is presented below.   As at 2010 at least 261 cases have been genetically confirmed and are seen in hospital-based PWS clinics.  One in 17 000 would be a conservative estimate of the birth incidence in the past two decades.  Another 79, mainly older individuals with PWS are known to the Prader-Willi Syndrome Association of Australia. Information on adults diagnosed with PWS is scarce and the total number of adult patients seen by specialists or general practitioners is currently unknown. Diagnosis of adults may be based on clinical characteristics only, which are not always confirmed genetically.

Number of people with Prader-Willi syndrome by year of birth in Australia since 1955
Data from the Australian Prader-Willi syndrome database and the Prader-Willi Syndrome Association of Australia