We conducted a systematic review and meta-analysis of double-blind randomized controlled trials to quantify the dose-related systolic (SBP) and diastolic blood pressure (DBP) lowering efficacy of renin inhibitors vs placebo in the treatment of adults with primary hypertension. Databases searched were Medline (1966-March 2008), EMBASE (1988-March 2008) and Cochrane Central Register of Controlled Trials (CENTRAL). Six trials in 3694 patients met the inclusion criteria. All examined aliskiren, the only renin inhibitor licensed for marketing in Canada and the United States. Aliskiren caused a dose-related SBP/DBP lowering effect compared to placebo: weighted mean difference with 95% CI: aliskiren 75 mg, -2.9 (-4.6, -1.3)/-2.3 (-3.3, -1.3) mm Hg; aliskiren 150 mg, -5.5 (-6.5, -4.4)/-3.0 (-3.7, -2.3) mm Hg; aliskiren 300 mg, -8.7 (-9.7,-7.6)/-5.0 (-5.6, -4.3) and aliskiren 600 mg, -11.4 (-13.5, -9.2)/-6.6 (-7.9, -5.2) mm Hg. Aliskiren 300 mg significantly lowered both SBP -3.0 (-4.0, -2.0) and DBP -1.7 (-2.3, -1.0) as compared to aliskiren 150 mg. Aliskiren has no effect on blood pressure variability. No data were available to assess the effect of aliskiren on heart rate or pulse pressure. This review found weak evidence that during 4- to 8-week use, aliskiren did not increase withdrawals due to adverse effects as compared to placebo. We concluded that aliskiren has a dose-related blood pressure lowering effect better than placebo and magnitude of effect is similar to that determined for angiotensin-converting enzyme inhibitors and angiotensin receptor blockers.