BACKGROUND The first step in the diagnosis of lung cancer is for individuals in the general population to recognise respiratory alarm symptoms (RAS). Knowledge is sparse about RAS and factors associated with experiencing RAS in the general population. This study aimed to estimate the prevalence of RAS in the general population, and to analyse possible associations between lifestyle factors and experiencing RAS. METHODS A web-based survey comprising 100 000 individuals randomly selected from the Danish Civil Registration System. Items regarding experience of RAS (prolonged coughing, shortness of breath, coughing up blood and prolonged hoarseness) and self-reported lifestyle factors (smoking status, alcohol intake and body mass index) were included in the analysis. RESULTS A total of 49 706 individuals completed the questionnaire. 16 per cent reported at least one RAS. Prolonged coughing (8.4%) and shortness of breath (8%) were most prevalent, while coughing up blood was least prevalent (0.1%). More men than women reported RAS (p<0.001). Odds of reporting RAS increased with age (Ptrend<0.001). In men and women, former and current smoking was associated with reporting at least one RAS (former smoking: ORmen=1.42, 95% CI 1.39 to 1.56; ORwomen=1.25, 95% CI 1.15 to 1.36; current smoking: ORmen=2.58, 95% CI 2.35 to 2.83; ORwomen=2.45, 95% CI 2.25 to 2.68). Individuals who were underweight or obese were significantly more likely to report at least one RAS. Odds of reporting at least one RAS increased with increasing alcohol intake for both genders (Ptrend<0.001). CONCLUSIONS RAS are common in the general population. Men experience more symptoms than women, and prevalence increases with age. Being a former or current smoker and being underweight or obese are positively associated with experiencing RAS. The likelihood of experiencing RAS increases with increasing alcohol intake. Future research should investigate healthcare seeking for RAS among individuals with different lifestyles.