Background and Objectives: Studies on the relationship between Alzheimer’s disease (AD) and health care costs have yielded conflicting results. This study analyzed the relationship between co-morbid conditions and health care utilization and costs for patients with AD and estimated costs by stage of disease and receipt of pharmacotherapy. Methods: We conducted a retrospective analysis of administrative data for 1,366 patients with AD and 13,660 age-gender matched controls enrolled in a large Medicare managed care organization (MCO). Co-morbid conditions were based on the diagnostic classifications from the Charlson co-morbidity index. Health care costs and utilization for MCO-covered services for cases were compared to controls. We used presence of complications of AD associated with later-stage disease to classify patients as having earlier-or later-stage AD. Results: After controlling for co-morbid conditions, age, and gender, annual costs were $3,805 higher for AD patients, resulting in excess costs of $5 million to the MCO. For seven of the 10 most prevalent co-morbidities for AD patients, adjusted costs were higher for AD patients compared with controls with the same condition. Higher costs were attributable to higher inpatient and skilled nursing facility costs. Costs for patients classified as earlier-stage AD were 44% higher than controls and significantly higher for eight of 10 co-morbid conditions when compared with controls with the same conditions. Costs for AD patients receiving treatment by a cholinesterase inhibitor were $2,408 lower than AD patients not receiving therapy. Conclusions: Utilization and costs for patients with AD were higher compared to controls and were substantially higher for patients with both AD and co-morbid diseases commonly targeted for disease management. Earlier-stage AD and receipt of pharmacotherapy were associated with lower costs. These findings indicate that better treatment and care management of AD could reduce the costs of co-morbid illnesses commonly suffered by AD patients.