We evaluated the efficacy and safety of the centrally acting cholinesterase inhibitor, rivastigmine tartrate, for patients with mild to moderately severe Alzheimer's disease (AD) with or without concurrent vascular risk factors (VRF). Patients (45-90 years of age) were randomized to placebo (n = 235), low-dose rivastigmine (1-4 mg/day, n = 233), or high-dose rivastigmine (6-12 mg/day, n = 231) for 26 weeks. Efficacy measures included the Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog), the Clinician's Interview Based Impression of Change (CIBIC-Plus), the Progressive Deterioration Scale (PDS), the Global Deterioration Scale (GDS), and the Mini-Mental State Examination (MMSE). For efficacy and safety analysis, patients were categorized by baseline Modified Hachinski Ischemic Score (MHIS) for the determination of VRF (MHIS > 0: presence of VRF; MHIS = 0: absence of VRF). As early as 12 weeks, the mean change from the baseline ADAS-Cog score was significantly different for those patients treated with high-dose rivastigmine compared with placebo controls in both MHIS categories. However, the treatment difference between high-dose rivastigmine and placebo at each time-point was larger for patients with MHIS > 0. The proportion of responders was significantly greater in the high-dose rivastigmine group for each level of improvement. No differences were noted between treatment groups regarding safety evaluations. Rivastigmine is effective in both categories of patients, and those with VRF experience greater clinical benefit (cognition, activities of daily living, and disease severity).