BACKGROUND Previous studies of Ginkgo biloba extract (GbE) in patients with various forms of cognitive impairment or dementia have shown promising results. OBJECTIVE To determine the clinical efficacy of GbE in mild to moderate dementia of the Alzheimer type. METHODS Randomized, placebo-controlled, double-blind, parallel-group, multicenter trial. METHODS Outpatient clinics of universities and private research centers specialized in dementia. METHODS 513 outpatients with uncomplicated dementia of the Alzheimer's type scoring 10 to 24 on the Mini-Mental State Examination and less than 4 on the modified Hachinski Ischemic Score, free of other serious illnesses and not requiring continuous treatment with any psychoactive drug. METHODS 26-week treatment with GbE at daily doses of 120 mg or 240 mg or placebo. RESULTS Cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog), Alzheimer's Disease Cooperative Study Clinical Global Impression of Change (ADCS-CGIC). RESULTS There were no significant between-group differences for the whole sample. There was little cognitive and functional decline of the placebo-treated patients, however. For a subgroup of patients with neuropsychiatric symptoms there was a greater decline of placebo-treated patients and significantly better cognitive performance and global assessment scores for the patients on GbE. CONCLUSIONS The trial did not show efficacy of GbE, however, the lack of decline of the placebo patients may have compromised the sensitivity of the trial to detect a treatment effect. Thus, the study remains inconclusive with respect to the efficacy of GbE.