Presymptomatic infants diagnosed through neonatal screening for cystic fibrosis can have biochemical evidence of malnutrition. With aggressive dietary management and treatment with pancreatic enzymes, normal biochemical indices of nutrition can be achieved at 12 months of life in most cases. Males with cystic fibrosis appear to be more at risk than females for abnormal growth and biochemical indices of nutrition in the first year of life. This may be related to the observed decrease in fat intake when compared to females. Males, especially, should be carefully observed for development of nutritional abnormalities based on this data. Careful attention should be paid to vitamin E and essential fatty acid status in all CF infants. The numbers in this study are small and the long-term consequences of early nutritional intervention await the conclusion of the randomized, controlled study on-going in Wisconsin.