The objective of this study was to compare postnatal growth and clinical outcomes of preterm infants after an adjustment in amino acid and lipid administration practice. The study was conducted retrospectively in preterm infants with a birth weight < 1250 g for the periods January-June 2007 and June-November 2010. In 2007, amino acid solution was initiated at 2 g/kg/ day on the first day of life and advanced 1 g/kg/day to a maximum of 3 g/kg/day; lipid solution was initiated at 1 g/kg/day on the first day of life and advanced 0.5 g/kg/day to a maximum of 2 g/kg/day (low-dose parenteral nutrition group). In 2010, amino acid solution was initiated at 3 g/kg/day on the first day of life and advanced 1 g/kg/day to a maximum of 4 g/kg/ day; lipid solution was initiated at 1 g/kg/day on the first day of life and advanced 1 g/kg/day to a maximum of 3 g/kg/day (high-dose parenteral nutrition group). Patient characteristics were similar in the two groups. Infants in the high-dose parenteral nutrition group showed a significant reduction in the time needed to regain birth weight and a significant reduction in the maximum weight loss. Weight, length and head circumference at discharge were significantly higher in the high-dose parenteral nutrition group. The mean duration of parenteral nutrition, mean number of days to reach full enteral feeding and incidence of sepsis and necrotizing enterocolitis were significantly lower in the high-dose parenteral nutrition group. There was no significant difference in the mortality rate between the groups. In conclusion, a more aggressive parenteral nutrition protocol for preterm infants resulted in a more rapid increase in weight, length and head circumference, and decreased incidence of sepsis and necrotizing enterocolitis.