A case-control study assessed factors associated with HIV infection among cases (59 persons aged 50 years or older at HIV diagnosis) and controls (59 self-reported uninfected persons aged 50 years and older) from Southern Brazil. Participants answered a 142-item questionnaire that included queries on demographic characteristics, sexual behavior, substance use, and knowledge about HIV/AIDS. The participants' age ranged from 50 to 87 years and 75.4% were women. A multivariate analysis demonstrated that cases had higher odds of being male, having lower incomes, and reporting STDs. The study reinforces that HIV infection among the population aged 50 years and older is related to demographic characteristics and sexual behavior. Once mainly prevalent among younger persons, HIV/AIDS is now manifesting increasingly in older adults. This indicates the need for health care professionals to not overlook important aspects of older persons' lives. Sexuality, for example, is an important part of the life cycle. It cannot be ignored in this population.