Some clinicians believe that spinal manipulation is an effective treatment for asthma. The aim of this systematic review was to critically evaluate the evidence for or against this claim. Four electronic databases were searched without language restrictions from their inceptions to September 2008. Bibliographies and departmental files were hand-searched. The methodological quality of all included studies was assessed with the Jadad score. Only randomised clinical trials of spinal manipulation as a treatment of asthma were included. Three studies met these criteria. All of them were of excellent methodological quality (Jadad score 5) and all used sham-manipulation as the control intervention. None of the studies showed that real manipulation was more effective than sham-manipulation in improving lung function or subjective symptoms. It is concluded that, according to the evidence of the most rigorous studies available to date, spinal manipulation is not an effective treatment for asthma.