Growth failure is common among premature infants and carries the risk of delayed cognitive development. Its immediate cause is almost always inadequate intake of protein. But the reason why protein intake is insufficient changes with time. In the first days of life, when nutrition is predominantly provided parenterally, hesitation to provide the necessary high intakes of amino acids for a sufficient length of time is the main cause. When feedings are provided enterally, frequent interruptions of feedings and insufficient protein fortification of human milk are the main causes. Close monitoring of growth alerts the neonatologist to impending growth failure and permits remedial action.