In low-income countries, undernutrition and infectious diseases are major health problems. Their coexistence is partly due to poverty being an important determinant of both problems, but also due to the two-way causal interactions between nutritional deciencies and infections, whereby infections exacerbate nutritional deciencies, which in turn increase infectious disease morbidity and mortality. Most research has been conducted on the relationship between generalized malnutrition or micronutrient deciencies and childhood infections. Control of infectious diseases is now considered important in prevention of undernutrition, and evidence-based nutritional interventions have been established to reduce childhood morbidity and mortality.