Background: Asthma is defined by variable respiratory symptoms and lung function, and may influence work ability. Similarly, obesity may contribute to respiratory symptoms, affect lung function, and reduce work ability. Thus, assessment of the influence of obesity on work ability, respiratory symptoms, and lung function in adults with asthma is needed. Objectives: We hypothesized that patients with obesity and asthma have more respiratory symptoms and reduced work ability and lung function compared with normal-weight patients with asthma. Methods: We examined 626 participants with physician-diagnosed asthma, aged 18-52 years, recruited from a cross-sectional general population study using a comprehensive questionnaire including work ability score, the asthma control test (ACT), height and weight, and spirometry with reversibility testing. Results: Participants with a body mass index (BMI) ≥30 kg/m<sup>2</sup> (i.e., obese) had a higher symptom score (OR 1.78, 95% CI 1.14-2.80), current use of asthma medication (1.60, 1.05-2.46), and incidence of ACT scores ≤19 (poor asthma control) (1.81, 1.03-3.18) than participants with BMI ≤24.9 kg/m<sup>2</sup> (i.e., normal weight). Post-bronchodilator forced vital capacity (FVC) as a percentage of predicted (β coefficient -4.5) and pre-bronchodilator forced expiratory volume in 1 s as a percentage of predicted (FEV<sub>1</sub>) (β coefficient -4.6) were negatively associated with BMI ≥30 kg/m<sup>2</sup>. We found no statistically significant association of BMI >30 kg/m<sup>2</sup> (compared to BMI <24.9 kg/m<sup>2</sup>) with sick leave (1.21, 0.75-1.70) or reduced work ability (1.23, 0.74-2.04). Conclusions: There were indications that patients with obesity had a higher symptom burden, poorer asthma control, higher consumption of asthma medication, and reduced lung function, in particular for FVC, compared with normal-weight patients.