OBJECTIVE To evaluate the efficacy and safety of eptastigmine as a treatment for patients with mild-to-moderate Alzheimer's disease (AD). METHODS The study was designed as a randomized, double-blind, placebo-controlled, parallel-group study. It was performed in 26 Italian and American geriatric and neurological centers. The study group comprised 349 outpatients with a diagnosis of probable AD according to the criteria of the National Institute of Neurological and Communicative Disorders and Stroke and the AD and Related Disorders Association. Patients were assigned to one of the three study groups: placebo (n = 119), eptastigmine 10 mg t.i.d. (n = 115) or eptastigmine 12 mg t.i.d. (n = 115) for 25 weeks. The AD Assessment Cognitive Subscale (ADAS-Cog) and the Clinical Dementia Rating Scale-Sum of the Boxes (CDR-SB) were the primary outcome measures for efficacy. RESULTS The two doses of eptastigmine produced similar results and are presented together. Percentages of patients completing double-blind treatment were 82 and 87% in the placebo and eptastigmine groups, respectively. At the end of treatment, the intent to-treat analysis on 342 patients showed a statistically significant effect of eptastigmine compared to placebo on both ADAS-Cog (p = 0.047) and CDR-SB (p = 0.010). Patients on eptastigmine performed significantly better than placebo-treated patients also on the Mini-Mental State Examination (p < 0.001). The drug was well tolerated with 5% of patients withdrawing due to adverse events versus 3% on placebo. Adverse events were recorded in 46% of the patients on placebo compared to 52% of the patients taking eptastigmine. Cholinergic side effects (nausea, vomiting, diarrhea and abdominal pain) were reported with similar frequency in the eptastigmine and placebo-treated patients. CONCLUSIONS Eptastigmine doses up to 12 mg t.i.d. for 25 weeks are well tolerated. The drug positively affects cognitive performance and global function of patients with mild-to-moderate AD.