We reviewed the benefits and harms of augmentation therapy with alpha-1 antitrypsin in patients with alpha-1 antitrypsin deficiency and lung disease. We searched for randomised trials comparing augmentation therapy with placebo or no treatment in PubMed and ClinicalTrials (7 January 2010). Two trials were included with a total of 140 patients. The trials ran for two to three years. Mortality data were not reported. There was no information on harms in the first trial; in the second trial, serious adverse events were reported in ten of 38 patients in the drug group and in 18 of 39 patients in the placebo group. Annual number of exacerbations and quality of life were reported in the second trial and were similar in the two groups. The meta-analyses showed that forced expiratory volume in one second deteriorated a little more in the drug group than in the placebo group (difference -20 ml per year; 95% confidence interval -41 to 1; p = 0.06). For carbon monoxide diffusion, the difference was -0.06 mmol/min./kPa per year (95% confidence interval -0.17 to 0.05; p = 0.31). Lung density measured by computed tomography deteriorated a little less in the drug group than in the placebo group (difference 1.14 g/l; 95% confidence interval 0.14 to 2.14; p = 0.03) over the total course of the trials. Augmentation therapy with alpha-1 antitrypsin cannot be recommended in view of the lack of evidence of clinical benefit and the cost of treatment.