Background and objective: Chronic respiratory symptoms (in particular, breathlessness and cough) can cause physical, social and emotional distress, and may indicate the presence of an underlying disease that presages future poor health outcomes. Our aim was to investigate the burden of breathlessness in Australian adults, including breathlessness that may be undiagnosed, unlabelled or untreated. Methods: The National Breathlessness Survey was a cross-sectional, web-based survey conducted in October 2019. Australian adults were randomly selected from a large web-based survey panel with recruitment stratified by age-group, gender and state of residence according to national population data. The main outcome measures were modified Medical Research Council (mMRC) dyspnoea scale, EuroQol visual analog scale, Dyspnoea-12 score and 4-item Patient Health Questionnaire (PHQ-4). Results: Among all respondents (n��=��10,072; 51.1% female; median age group 40���49 years), 9.5% reported clinically important breathlessness (mMRC dyspnoea grade ��� 2, 2��=�����I walk slower than people of the same age on the level because of breathlessness or have to stop for breath when walking at my own pace on the level���). Among those with clinically important breathlessness, 49.1% rated their general health as fair or poor and 44.2% had at least moderate depression or anxiety symptoms (PHQ ��� 6) but over half (50.8%) did not report a current respiratory or heart condition diagnosis. Conclusion: Breathlessness is common among Australian adults, and is associated with a substantial burden of ill health, including among people without a diagnosed respiratory or heart condition. The extent of underdiagnosis of these conditions or alternative causes of breathlessness requires further investigation.