Aim: The purpose of this study was to conduct a systematic review of randomized controlled trials where the efficacy of psychological interventions in modifying health and behavioural outcomes for adults with asthma was investigated. Method: A review of randomized controlled trials was designed. The literature search was conducted until May 2005. Results: Fourteen studies, involving 617 adults, were included in the review. The use of 'as needed' medications was reduced by relaxation therapy (OR 4.47, CI 1.22-16.44), quality of life, measured using the Asthma Quality of Life Questionnaire, showed a positive effect following cognitive behavioural therapy (WMD 0.71, CI 0.23-1.19), and peak expiratory flow outcome data indicated a significant difference in favour of bio-feedback therapy (SMD 0.66, CI 0.09-1.23). Conclusions: Some promising results did emerge from meta-analyses performed. However, due to heterogeneity and the low quality of included studies, this review was unable to draw firm conclusions for the role of psychological interventions in asthma. We recommend that larger and well-conducted randomized trials use valid outcome measures to evaluate the effectiveness of psychological interventions for adults with asthma.