Comprehensive recommendations for the assessment and control of vitamin A deficiency (VAD) were rigorously reviewed and revised by a working group and presented for discussion at the XX International Vitamin A Consultative Group meeting in Hanoi, Vietnam. These recommendations include standardized definitions of VAD and VAD disorders. VAD is defined as liver stores below 20 micro g (0.07 micro mol) of retinol per gram. VAD disorders are defined as any health and physiologic consequences attributable to VAD, whether clinically evident (xerophthalmia, anemia, growth retardation, increased infectious morbidity and mortality) or not (impaired iron mobilization, disturbed cellular differentiation and depressed immune response). An estimated 140 million preschool-aged children and at least 7.2 million pregnant women are vitamin A deficient, of whom >10 million suffer clinical complications, principally xerophthalmia but also increased mortality, each year. A maternal history of night blindness during a recent pregnancy was added to the clinical criteria for assessing vitamin A status of a population, and the serum retinol criterion for a "public health problem" was revised to 15% or more of children sampled having levels of <20 micro g/dL (0.7 micro mol/L). Clinical trials and kinetic models indicate that young children in developing countries cannot achieve normal vitamin A status from plant diets alone. Fortification, supplementation, or other means of increasing vitamin A intake are needed to correct widespread deficiency. To improve the status of young infants, the vitamin A supplements provided to mothers during their first 6 wk postpartum and to young infants during their first 6 mo of life should be doubled.