The SUN Study is designed to enroll and follow for 5 or more years a cohort of up to 1,000 HIV-infected adults at HIV specialty care centers in four U.S. cities: Denver, Minneapolis, Providence, and St. Louis. Data will be gathered through longitudinal real-time chart review, biannual physical examination (e.g., body mass index [BMI], blood pressure), repeated non-invasive imaging (e.g., dual energy x-ray absortiometry [DEXA] scanning, carotid ultrasonography) and regularly scheduled laboratory testing (e.g., serum lipids, pap smears, and urinary microalbumin). Data collection and quality control will be managed by Cerner Corporation. After sufficient enrollment, (circa 200 persons per site) a structured prevention program to reduce HIV transmission will be introduced. The impact of this intervention will be evaluated both subjectively (e.g., self-reported change in behavior on an audio computer-assisted self-interviewing [ACASI] questionnaire) and objectively (e.g., change in sexually transmitted disease [STD] incidence).