Background: Adult-onset asthma is less studied than asthma with onset in childhood and is associated with poor asthma control. Aim: To study the association between uncontrolled adult-onset asthma and clinical biomarkers as well as comorbidities in middle-aged and elderly individuals. Methods: In 2019-2020 a population-based adult-onset asthma cohort (n=227) underwent a structured interview, asthma control test (ACT), spirometry, skin prick test, blood sampling and measurement of exhaled fractional nitric oxide. Analyses were performed among all included as well as separately in middle-aged (37-64y, n=120) and older (?65y, n=107) participants. Results: Uncontrolled asthma (ACT?19) was associated with a blood neutrophil count ?5/µl, BMI?30 and several comorbidities among all participants. Reflux, malignancy and ischemic heart disease (IHD) were more prevalent among the elderly compared to middle-aged, while allergic rhinitis was more prevalent in the middle-aged. When adjusted for sex and smoking, BMI?30 (OR 3.04; 1.24-7.50), eosinophils ?0.3/µl (OR 3.17; 1.20-8.37), neutrophils ?5/µl (OR 4.39; 1.53-12.62) and allergic rhinitis (OR 5.10; 1.59-16.30) were associated with uncontrolled asthma in the middle-aged. Among the older adults, uncontrolled asthma was only associated with comorbidities: chronic rhinitis (OR 4.08; 1.62-10.31), IHD (OR 3.59; 1.17-10.98), malignancy (OR 3.10; 1.10-8.73) and depression/anxiety (OR 16.31; 1.82-146.05). Conclusions: In adult-onset asthma, clinical biomarkers including eosinophils and neutrophils in blood were associated with uncontrolled asthma among middle-aged, while comorbidities were associated with uncontrolled asthma in the elderly.