The aim of this longitudinal study was to compare the changes in somatic and basic motor development of Hungarian elementary school boys between 7 and 10 years of age. The subjects (n=226) were volunteer, non-athletic elementary school boys from 15 Budapest public schools. The children, qualified as healthy by a school physician in September 2002, were divided into two subgroups according to percent body fat: G1: normal body weight (Fat%<25, n=186); G2: overweight and obese (Fat%>25, n=40). Body height, body mass, 5 skinfold thicknesses and 4 motor performance scores (30m dash, standing broad jump, ball throw and 400m run) were measured twice per year (in October and April) between October 2002 and April 2005. The within group changes for 6 age groups were tested by repeated ANOVA. The inter-group differences were analysed by t-tests for independent samples. The differences between the group means were significant except for the chronological age and the ball throw. The members of G2 were significantly taller initially (at the time of first data collection), and their motor performances were consistently lower [t(df=224) = 6.53, p < .001 for 30m dash; t(df=224) = 5.43, p < .001 for standing broad jump]. The patterns of somatic development (described by the relative differences between the measures) were parallel; while the mean differences between the motor performance scores—with few exceptions—increased with each observation. The running and standing broad jump performances for G2 did not appreciably change, but in fact, actually decreased over the course of the last 3 investigations. In addition, although the relative body fat content of the two groups at the time of the final investigation differed sharply (20.1% and 33.5% for G1 and G2, respectively, t(df=224) = 14.10, p < .001, it is important to note that even the normal group boys gained an appreciable amount of body fat—from 15.25% to 20.14%—over the course of just three years F(df=1,185) = 156.9, p < .001. Compared to a previous study (Eiben et al., 1992), the significantly higher relative body fat content observed in the present study is consistent with the emerging pattern of childhood obesity as detailed in the most recent Hungarian representative growth study (Mészáros et al., 2005).Keyword(s): exercise/fitness, physical activity