Background & aims: Accurate field methods to assess body composition in young children are scarce. The aim of this study was to validate bioelectrical impedance analysis with deuterium based total body water analysis in (pre)school children. Methods: We examined fifty-six 4-7 year old children, 36% boys. Total body water estimated with standardized single frequency bioelectrical impedance analysis was compared with deuterium dilution technique. An established equation (Kushner) was tested, recalibrated and subsequently cross-validated in an independent sample. Results: Compared to deuterium dilution (mean total body water 12.66 kg, n = 56), bioelectrical impedance analysis underestimated total body water by 0.51 kg (p = 0.002) and this varied across the range of total body water (r = 0.41; p = 0.002). Recalibration of the equation yielded: total body water (kg) = 0.439 Height2 (cm2)/Resistance (Ω) + 0.027 Weight (kg) + 4.014 (R2 = 0.74, SEE = 0.96 kg). Application of this equation in the independent sample (n = 20) showed a non-significant bias in total body water (mean bias -0.30 kg, p = 0.17). Conclusions: These data indicate that BIA underestimates total body water by 0.51 kg in (pre)school children, when using the Kushner equation. Recalibration and cross-validation enables enhanced assessment of body composition in (pre)school children for use in epidemiological field studies.