An important focus of attention in Public Health has been micronutrient deficiency in human being because of the enhanced vulnerability of individuals to the effects of micronutrient deficiency or imbalance. Among all micronutrients deficiencies, vitamin A has been one of the most important public health problems, affecting a large percentage of people in developing countries. Vitamin A is particularly important for its role in the process of organism defense against infections. This article reviews comprehensively vitamin A metabolism, it highlights hypovitaminosis A relationship with pregnancy and human imunodeficiency, showing its repercussions in several clinical conditions.