The objective of this study was to assess the effect of dexamethasone on growth, body composition and protein metabolism using the piglet as a model for rapidly growing premature infants. Seven-day-old male pigs (n = 18) were randomized to 0.5 mg/kg/day oral dexamethasone or placebo for 15 consecutive days. Weight and length gains and weight gained per energy or protein consumed were significantly lower in the dexamethasone group. Serum urea nitrogen was significantly higher in the dexamethasone group by day 15 of the study. No differences were observed between groups for urinary creatinine. The whole body percent lean mass was significantly lower and percent fat mass was significantly higher in the dexamethasone piglets, as measured by dual energy X-ray absorptiometry. In young piglets, dexamethasone, at doses similar to those in premature infants, induces protein catabolism, impairs growth and alters its composition.