This is a cross-sectional analysis comparing the prevalence of AD in patients 60 years or older in the following 3 groups (which are each subdivided by the particular medication): (1) the entire population, (2) patients receiving statins, and (3) patients receiving medications used to treat hypertension or cardiovascular disease. The term "AD," as used for data in this article, refers to probable AD. To perform the study, we searched relational databases at 3 different hospitals (Loyola University Medical Center, Maywood, Ill, 22,143 medical records; Edward Hines Jr Veterans Affairs Hospital, Hines, Ill, 23,028 medical records; and Carl T. Hayden Veterans Affairs Medical Center, Phoenix, Ariz, 15,178 medical records) to obtain aggregate data about the frequency of AD. The relational databases allow correlational analysis of fields (such as diagnosis and medication) within a patient medical record from an aggregate patient database. The 3 databases are independent and do not overlap. The databases contain patient medical records, including information relevant to this study: age, sex, International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnoses, and medications history. Severity of disease was not present in the databases. For Edward Hines Jr Veterans Affairs Hospital and Carl T. Hayden Veterans Affairs Medical Center, the medical records describe patients who used the hospitals in the last 2 years (October 1, 1996, through August 31, 1998). Entries in the databases that contained patients' names but no medical information were excluded. Patients younger than 60 years were also excluded. Next we identified all patients who were taking 8 different medications (Table 1). Some of the patients may have received more than 1 medication or have had more than 1 diagnosis. We then determined the prevalence of AD or transient ischemic attacks (TIAs) for patients taking each medication. The patient searches were carried out using ICD-9-CM codes. Alzheimer disease was specifically identified under the code 331.0. However, as other codes also apply to AD, we included the following: 331.2 and 290.0, 290.10 to 290.13, 290.20, 290.21, and 290.3. Patients with TIAs were identified with ICD-9-CM codes: 434.00, 433.00, 433.10, 433.20, 435.0, and 435.2. Patients at each site who were being assessed for dementia were all seen or their medical records reviewed by the same attending neurologist or geriatrician (Loyola University Medical Center [G.G.C.]; Edward Hines Jr Veterans Affairs Hospital [G.S.]; and Carl T. Hayden Veterans Administration Medical Center [P.R.]). The diagnosis of AD was made according to the criteria of the National Institute of Neurology, Communicative Disorders, and Stroke–Alzheimer's Disease and Related Disorders Association11: clinical evidence of progressive dementia in more than 1 area of cognition in patients aged between 40 and 90 years, documentation of cognitive impairment by the Mini-Mental State Examination (MMSE), neuropsychological examination, and exclusion of other diagnoses by computed tomography or magnetic resonance imaging of the brain. The patients with the diagnosis of AD were all screened for other causes of their dementia. Each patient was screened for other metabolic, toxic, or affective disorders that may produce dementia. To screen for toxic or metabolic disorders, every patient with a putative diagnosis of AD underwent blood workup that included tests for VDRL findings and for thyrotropin, electrolytes, vitamin B12, folic acid, hepatic enzymes, serum creatinine, and serum urea nitrogen levels. Patients were screened for drug abuse, alcohol abuse, or affective disorder by clinical assessment. However, it is recognized that there may be considerable overlap of probable AD with ischemic white matter and subcortical nuclear lesions and leukoariosis as shown in prospective clinical longitudinal studies,12- 13 as well as overlap of definite AD with infarction on postmortem analyses. Thus, the diagnosis of probable AD by the usual conventional criteria does not exclude confounding vascular disease factors. In this study, the diagnosis of AD refers to probable AD and does not exclude the possibility of overlapping leukoariosis or ischemic white matter or subcortical nuclear lesions.