In all populations where vitamin A deficiency is an important public health problem, prophylactic vitamin A supplements should be given to all infants and young children (0-59 mo), pregnant women and postpartum women within 6 wk after delivery. The efficacy of vitamin A supplementation of young children is one of the best-proven, safest and most cost-effective interventions in international public health. The International Vitamin A Consultative Group (IVACG) also recommends that three 50,000-international unit (IU) doses of vitamin A should be given at the same time as infant vaccines during the first 6 mo of life. Recent kinetic studies have indicated that this regimen will be safe and is necessary to maintain the infant's vitamin A stores, even when the mother is also given 400,000 IU within the first 6 wk after delivery. IVACG will make a decision on whether to recommend prophylactic supplementation of all women of childbearing age when the results of two large trials in Ghana and Bangladesh are available. Active corneal xerophthalmia is always a medical emergency that should be treated with immediate high-dose vitamin A. High-dose vitamin A treatment is also recommended for infants and young children with xerophthalmia, severe malnutrition or measles. Low-dose vitamin A treatment is recommended for women with night blindness and/or Bitot's spots. Given the evidence of the cost-effectiveness of vitamin A supplementation, it is essential that effective vitamin A supplementation programs are made universally available to all populations where vitamin A deficiency is an important public health problem.