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Densitometric, 40K and skinfold estimates of per cent total body fat were obtained on 49 prepubescent boys, 8 to 11 years of age, to evaluate the relative applicability of these procedures to this age group. No significant differences were found between the mean % fat estimates obtained by different methods on the total group of boys, but 40K estimates of fatness in certain individuals underestimated those obtained using the other methods. Associations between the % fat estimates were only moderate with correlations ranging from .74 to .77. Much of the discrepancy between methods was found to be due to technical rather than biological variation. Technical errors of 3.0, 1.6 and .5% fat were estimated for per cent fat based on body potassium, body density and skinfold thickness measures, respectively.A closer association was found between the density and 40K estimates of fat-free weight (rzz.94) and fat weight (r = .91) than to % fat, due primarily to the larger range of values of the absolute as compared to the percentage estimates. In general, the procedures for estimating body composition utilized in this study appear to be applicable to children, but sizable differences in individual estimates warrant caution when applying these methods to individual children.