This is a long-term (2-year), randomized (patients will be assigned to treatment by chance), double blind (neither the physician nor the patient will know which treatment is assigned) study of galantamine versus placebo in subjects with mild to moderately-severe AD. Approximately 2,000 patients will participate in this study. The study length for each patient is approximately 25.5 months. The study consists of 3 phases: a pretreatment phase, a treatment phase, and a posttreatment phase. The pretreatment phase includes a 2-week screening period (to obtain a patient's and his or her caregiver's informed consent and to confirm eligibility for the study) and a baseline visit at which subjects will be randomly assigned, in a 1 to 1 ratio, to receive either galantamine or placebo once a day in the morning. Study drug will first be dispensed at the baseline visit. The treatment phase is composed of a titration period (the study drug will be introduced gradually) and a maintenance period and includes 9 visits (3 of which are conducted by telephone). The titration period is 12 weeks long, and visits occur about every 28 days. In the first 4 weeks of the titration period, subjects will receive either 8 mg galantamine or matching placebo, and this dose will be increased to 16 mg galantamine or placebo in the second 4 weeks. The dose will then be increased to 24 mg galantamine or placebo for the final 4 weeks of the titration period if the investigator believes the subject will benefit from and will safely tolerate 24 mg/day. If not, the subject may continue to receive 16 mg galantamine or placebo through the end of the titration period. After the titration period, subjects will enter the maintenance period and continue to take study drug at the dosage they received at the end of the titration period. This dosage may be continued through the end of the study or may be changed once (either up from 16 to 24 mg or down from 24 to 16 mg), depending upon the benefit and the safety of such a change for the individual patient as judged by the investigator. No dosage will exceed 24 mg/day. The posttreatment phase includes an End-of-Study Visit that occurs at the end of the maintenance period. A follow-up telephone contact (interview) is conducted 1 month after the End-of-Study Visit. The effectiveness of galantamine will be evaluated using the following tools: the Mini-Mental State Examination (MMSE); the Disability Assessment in Dementia (DAD); and the Assessment of Patient Accommodation Status and Caregiver Burden (APAS CarB). Safety evaluations for the study include the monitoring of vital status and institutionalization status, adverse events, vital signs, weight, physical and neurologic examinations. A Data Safety Monitoring Board, external to the company, has been commissioned for this study to monitor the progress of the study and to ensure that the safety of patients is not compromised. The effectiveness hypothesis of this study is that galantamine, 16 to 24 mg per day, is superior to placebo in reducing cognitive decline from baseline (start of study drug) as measured by the MMSE over the course of 2 years. The safety hypothesis is that the mortality rate in the galantamine 16 to 24 mg per day treatment group will be the same as that in the placebo group over the course of 2 years.