We present preliminary results of a cross-sectional study which had the following objectives: 1--to develop percentile curves of weight, height and head circumference of Portuguese children with Trisomy 21 from 0 to 48 months of age; 2--a comparison of the growth of children with Trisomy 21 with a control population of their siblings, and 3--a comparison between the growth of Portuguese and American children with Trisomy 21 (based on the data of Cronk et al). We conclude that: 1--there is growth delay (weight, height, head circumference) in the Portuguese children with Trisomy 21, in all of the parameters evaluated and in all age groups; 2--Portuguese children with Trisomy 21 present values similar to those obtained by Cronk et al until 24 months of age; 3--from the age of 30 months onward Portuguese children with Trisomy 21 were heavier and taller than American children with Trisomy 21. This supports the usefulness of percentile curves specifically for Portuguese children with Trisomy 21.