The objective of the study was to find predictors for work disability among adults with recent-onset asthma. The study was performed in a group of 332 subjects with recent-onset asthma. The predictors were ascertained by structured interviews, pulmonary function measurements, methacholine challenge tests and skin prick tests. Asthma severity was classified into mild, moderate or severe, based on the minimum medication required to maintain asthma control. Work ability was based on self-assessment by inquiring about the subjects' present work ability, expressed in percent. The self-reported work ability decreased significantly with increasing number of days off work, indicating that self-reported work ability reflects the actual work ability. The majority (56%) of the subjects reported 100% working ability. Among women, but not among men, working ability was negatively correlated (rs = -0.33) with age. Among subjects with PC20 < 16 mg ml-1 work ability increased with increasing PC20. There was no relation between FEV1, FVC and working ability. Asthma severity and current respiratory symptoms at the work place showed a significant negative relation with work ability. In a logistic regression model, when controlling for age, gender, smoking and weekly working hours, decreased work ability was associated with asthma severity, respiratory symptoms at the workplace and PC20 < or = 4 mg ml-1. In conclusion, the work ability was assessed as normal in most asthmatic subjects. Significant predictors for decreased work ability were asthma severity, workplace-associated respiratory symptoms and bronchial hyperresponsiveness. The results indicate that work ability among asthmatics could be improved by reducing the workplace-associated symptoms, either by reducing the exposure to triggers or by improving the asthma therapy.