Human immunodeficiency virus (HIV) infection is a major public health problem worldwide, but particularly in subsaharan Africa and Asia. Numerous observational studies report inverse associations between vitamin status, measured biochemically or as levels of dietary intake, and the risk of disease progression or vertical transmission. Evidence to support these findings has been obtained from a few randomized placebo-controlled trials. In this paper, we review studies that examined the role of vitamins A, B, C, D, and E in HIV disease progression and transmission, and we discuss the potential mechanisms of action of these vitamins. Adequate vitamin intake leads to enhancement of epithelial integrity and systemic immunity and could contribute to improved clinical condition among HIV-infected subjects and reduce vertical transmission by reducing the risk and severity of opportunistic infection and reducing viral load in blood. Adequate vitamin status may also reduce vertical transmission through the intrapartum and breastfeeding routes by reducing HIV viral load in lower genital secretions and breast milk, respectively. Vitamin supplements may be one of a few potential treatments that are inexpensive enough to be made available to HIV-infected persons in developing countries.