Preparations based on special extracts of the Ginkgo biloba tree are popular in various European countries. Previous studies have suggested the clinical efficacy of Ginkgo in patients with dementia, cerebral insufficiency, or related cognitive decline. However, most of these studies did not fulfill the current methodologic requirements. We assessed the efficacy of the G. biloba special extract EGb 761 in patients with dementia and age-associated memory impairment in relation to dose and duration of treatment. Our study was a 24-week, randomized. double-blind, placebo-controlled, parallel-group, multicenter trial. Study participants were elderly patients with dementia (Alzheimer disease or vascular dementia) or age-associated memory impairment (AAMI). A total of 214 participants, recruited from 39 homes for the elderly in the Netherlands, were randomly allocated to Ginkgo (either 240 mg/d or 160 mg/d) or placebo (0 mg/d). After 12 weeks, the subjects in the two Ginkgo groups were randomized to continued Ginkgo treatment or placebo treatment. Primary outcome measures in this study were the Syndrome Kurz Test (SKT; psychometric functioning), the Clinical Global Impression of change (CGI-2; psychopathology, assessed by nursing staff), and the Nuremberg Gerontopsychological Rating Scale for Activities of Daily Living (NAI-NAA: behavioral functioning). One hundred twenty-three patients received Ginkgo (n = 79, 240 and 160 mg/d combined) or placebo (it = 44) during the 24-week intervention period. We found no statistically significant differences in mean change of scores between Ginkgo and placebo. The differences were SKT: +0.4 (90% confidence interval [CI] -0.9-1.7); CGI-2: +0.1 (90% CI -0.3-0.4), and NAI-NAA: -0.4 (90% CI -1.9-1.2). A positive difference is in favor of Ginkgo. Neither the dementia subgroup (n = 36) nor the AAMI subgroup (n = 87) experienced a significant effect of Ginkgo treatment. There was no dose-effect relationship and no effect of prolonged Ginkgo treatment. The trial results do not support the view that Ginkgo is beneficial for patients with dementia or age-associated memory impairment.