Long-term effects of multisensory stimulation were assessed using a “Snoezelen” room on older residents with dementia. Thirty patients were randomly assigned to 3 groups: multisensory stimulation environment (MSSE) group, individualized activities (activity) group, and control group. The MSSE and activity groups participated in two 30-minute weekly individualized intervention sessions over 16 weeks. Pre-, mid-, posttrial, and 8-week follow-up behavior, mood, cognitive, and functional impairment in basic activities of daily living were registered. Items included in the physically nonaggressive behavior factor improved significantly in post- versus pretrial in the MSSE group compared to the activity group, with no significant differences between MSSE and control groups. The MSSE and activity groups demonstrated behavior improvements and higher scores on the Cohen-Mansfield agitation inventory, verbal agitated behavior factor, and Neuropsychiatric Inventory–Nursing Home, with no significant differences between groups. The MSSE could have long-term positive effects on such neuropsychiatric symptoms in older people with dementia.