The four most important forms of malnutrition worldwide (protein-energy malnutrition, iron deficiency and anaemias (IDA), vitamin A deficiency (VAD), and iodine deficiency disorders (IDD)) are examined below in terms of their global and regional prevalences, the age and gender groups most affected, their clinical and public health consequences, and, especially, the recent progress in country and regional quantitation and control. Zinc deficiency, with its accompanying diminished host resistance and increased susceptibility to infections, is also reviewed. WHO estimates that malnutrition (underweight) was associated with over half of all child deaths in developing countries in 1995. The prevalence of stunting in developing countries is expected to decline from 36% in 1995 to 32·5% in 2000; the numbers of children affected (excluding China) are expected to decrease from 196·59millions to 181·92millions. Stunting affects 48% of children in South Central Asia, 48% in Eastern Africa, 38% in South Eastern Asia, and 13–24% in Latin America. IDA affects about 43% of women and 34% of men in developing countries and usually is most serious in pregnant women and children, though non-pregnant women, the elderly, and men in hookworm-endemic areas also comprise groups at risk. Clinical VAD affects at least 2·80million preschool children in over 60 countries, and subclinical VAD is considered a problem for at least 251millions; school-age children and pregnant women are also affected. Globally about 740million people are affected by goitre, and over two billions are considered at risk of IDD. However, mandatory salt iodisation in the last decade in many regions has decreased dramatically the percentage of the population at risk. Two recent major advances in understanding the global importance of malnutrition are (1) the data of 53 countries that links protein-energy malnutrition (assessed by underweight) directly to increased child mortality rates, and (2) the outcome in 6 of 8 large vitamin A supplementation trials showing decreases of 20–50% in child mortality.