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Longitudinal principal components analysis is used to summarize childhood trends in one measure of body fatness (W/S2) using pooled data from several large American longitudinal growth studies. For each of the age intervals analyzed (3 months-3 years, 3-9 years, 10-17 years and 4-18 years), component one represents magnitude or percentile level of W/S2 and component two represents change in percentile level of W/S2 from the beginning to the end of the age period. Components three through six represent more complicated patterns of change in W/S2 where percen­tile position fluctuates several times during the age interval analyzed. Information about continuity in W/S2 within and between the various age intervals can be discerned from the number of components retained and by correlations between component one scores from each of the age intervals. Intra-individual variation appears to be greater during infancy and adolescence than during childhood, and degree of continuity is greater between childhood and adolescence than between infancy and childhood. On the basis of both the number of components retained in the analyses of each age interval and the size of the correlations between component one scores for analyses at different age intervals, females appear to have a greater degree of continuity in W/S2 during childhood and adolescence than males.