Although many guidelines recommend regular exercise for adults with asthma, the empirical evidence on the effect of exercise on adult asthma has been inconsistent and there are no previous systematic reviews on this topic. To fill in this gap of knowledge, we synthesized the data on the effects of regular exercise on physical fitness, asthma control and quality of life of adult asthmatics. We performed a Medline search from 1980 through June 2011. In the systematic review we included all clinical trials that provided information on the effects of regular exercise on adult asthma. We conducted meta-analyses of maximal oxygen consumption (VO(2)max) and forced expiratory volume in 1 s (FEV(1)) based on 9 studies. A total of 11 studies were included in the analyses, but only 6 of them had a non-exercising reference group of asthmatics. The meta-analyses of randomized controlled trials showed that regular exercise significantly improved VO(2)max. There was no obvious improvement in lung function measurements. Some individual studies showed evidence of improvement in quality of life and asthma control. Meta-analyses provided evidence that regular physical exercise improves physical fitness of adult asthmatics. The results on effects on lung function were inconclusive. There is insufficient evidence to assess the effects of exercise on asthma control and quality of life.