If breast milk is not available during complementary feeding, 'follow-on' formula milk ensures a balanced intake of nutrients and is undoubtedly more suitable for infants than cows' milk. Formula milk provides a lower intake of proteins and saturated fats and a higher concentration of polyunsaturated fats, iron and zinc than cows' milk. In particular, delaying the introduction of cows' milk until the end of the first year of life, or even until after the second year, appears to play a fundamental role in the prevention of iron deficiency anaemia. It may also prevent excess weight gain and obesity and the development of immunoallergic symptoms, and may be important for neurobehavioural development. More than 30 varieties of follow-on formula milk are currently available in Italy alone. This review outlines the nutritional differences between breast, formula and cows' milks, and compares different brands of formula milk.