The objective of this review is to assess the clinical evidence for or against ginseng as a treatment for Alzheimer's disease (AD). We searched 20 databases from their inception to January 2009 and included all randomized clinical trials (RCTs) of any type of Panax ginseng to treat human patients suffering from AD. Methodological quality was assessed using the Jadad score. Two RCTs met all inclusion criteria. They assessed the effectiveness of ginseng as an adjunct to drug therapy on cognitive function compared with conventional drug therapy. Their results suggested significant effect in favor of ginseng on the Mini-Mental Status Examination (n = 174, weight mean difference (WMD), 1.85; 95% confidence intervals, CIs 0.88 to 2.82, P = 0.0002) and on the Alzheimer's Disease Assessment Scale (ADAS)-cognitive (n = 174, WMD, 3.09; 95% CIs 1.08 to 5.09, P = 0.003). Both of these studies are burdened with serious methodological limitations. In conclusion, the evidence for ginseng as a treatment of AD is scarce and inconclusive. Further rigorous trials seem warranted.