Blood pressure is often lower among patients with Alzheimer's disease (AD) compared to nondemented older adults. Lower blood pressure in AD correlates with reduced cerebral blood flow and cortical atrophy, but its effect on neuropsychological functioning is unclear. We assessed the effects of blood pressure on tests of dementia severity, attention, memory, language, verbal and nonverbal reasoning, motor/psychomotor functioning, and activities of daily living (ADL) among probable AD patients (n=609). As hypothesized, lower systolic blood pressure (SBP) predicted reduced attention (Digits Forward and Backward), memory (Visual Reproduction I), and ADLs. Unexpectedly, lower pulse pressure (SBP-DBP) predicted greater dementia severity (Mini-Mental State Examination, MMSE), attention (Digits Forward and Backward), memory (Logical Memory I and Visual Reproduction I), and ADLs. These findings may reflect a tendency for less severely demented patients to exhibit normal age-related changes in blood pressure, whereas abnormal patterns may develop with increased dementia severity.