['Asthma-onset in older individuals has been associated with an accelerated decline in lung function, but direct comparisons with younger adults have not been reported.', 'In a random population sample comprising 4983 individuals from the Copenhagen City Heart Study without asthma at baseline, we compared young (<35 years), middle-aged (35-64 years) and older (>64 years) adults with newly diagnosed asthma during a 10-year follow-up.', 'The proportion of cases with newly diagnosed asthma during follow-up was similar across age groups (Older adults: 7% (84/1168), middle-aged adults: 7% (223/3147), and young adults: 6% (42/668) (p\xa0=\xa0ns)). In all three age groups, lung function was reduced at baseline in subjects who were subsequently diagnosed with asthma, but most pronounced in those >35 years. (Mean FEV1%: Young 90.2% (±13.9), middle-aged 80.8% (±20.8), and older adults 80.8% (±24.2), p\xa0<\xa00.001). Furthermore, incident asthma was associated with an accelerated decline in lung function in older adults (young adults 11.0\xa0mL/year, middle-aged adults 18.2\xa0mL/year, and older adults 30.8\xa0mL/year). These differences were independent of FEV1 at baseline and smoking status, and were not explained by undiagnosed asthma in older adults, as the frequency of respiratory symptoms, including wheeze, was similar in all three age groups at baseline.'] Does lung function impairment increase with age of diagnosis in adult onset asthma?