In patients with dementia associated with Parkinson's disease (PD), the efficacy and safety of rivastigmine, an inhibitor of acetylcholinesterase and butyrylcholinesterase, were previously demonstrated in a 24-week double-blind placebo-controlled trial. Our objective was to determine whether benefits were sustained over the long term. Following the double-blind trial, all patients were permitted to enter an active treatment extension study, during which they received rivastigmine 3-12 mg/day. Standard safety assessments were performed. Efficacy assessments included the Alzheimer's Disease Assessment Scale cognitive subscale (ADAS-cog) and other measures of cognition, daily function, neuropsychiatric symptoms, and executive function. Of 433 patients who completed the double-blind trial, 334 entered and 273 completed the active treatment extension. At 48 weeks. the mean ADAS-cog score for the whole group improved by 2 points above baseline. Placebo patients switching to rivastigmine for the active treatment extension experienced a mean cognitive improvement similar to that of the original rivastigmine group during the double-blind trial. The adverse event profile was comparable to that seen in the double-blind trial. Long-term rivastigmine treatment appeared well tolerated and may provide sustained benefits in dementia associated with PD patients who remain on treatment for up to 48 weeks. (C) 2005 Movement Disorder Society.