Confusion and agitation in elderly patients are crucial problems. This study tested Gerdner's mid-range theory of individualized music intervention for agitation. An experimental repeated measures pretest-posttest crossover design compared the immediate and residual effects of individualized music to classical "relaxation" music relative to baseline on the frequency of agitated behaviors in elderly persons with Alzheimer's disease and related disorders (ADRD). Thirty-nine subjects were recruited from six long-term-care facilities in Iowa. The sample consisted of 30 women and 9 men (mean age 82 years) with severe cognitive impairment. Baseline data were collected for 3 weeks. Findings from the Modified Hartsock Music Preference Questionnaire guided the selection of individualized music. Group A (n = 16) received individualized music for 6 weeks followed by a 2-week "washout" period and 6 weeks of classical "relaxation" music. Group B (n = 23) received the same protocol but in reverse order. Music interventions were presented for 30 minutes, two times per week. The Modified Cohen-Mansfield Agitation Inventory measured the dependent variable. A repeated measures analysis of variance with Bonferroni post hoc test showed a significant reduction in agitation during and following individualized music compared to classical music. This study expands science by testing and supporting a theoretically based intervention for agitation in persons with ADRD.