Objectives: The one of the developing methods in paediatric densitometry field is peripheral quantitative computed tomography (pQCT), however, very little is known about its precision in children. The aim of presented study was to evaluate the precision errors for bone density, mass, dimensions, strength and mechanostat parameters as well as for soft tissue composition in children with medical conditions. Methods: Stratec XCT 2000L apparatus was used. The measurement sites were 4%, 14%, 38% and 66% of the lower leg length. The study group comprised of 60 patients (30 girls) aged 5,0-18,0 yrs. Results: Relative precision errors (CV%RMS) were from 0,25% for tibia 38% cortical bone density to 5,49% for fat cross-sectional area to muscle cross-sectional area ratio. Least significant change (LSC) was from 0,70% to 15,20%, respectively. Weak to moderate correlations between precision errors and body size, with r from -0,43 to 0,71, have been observed. Conclusion: Presented study revealed pQCT method at the lower leg in children with medical conditions as relatively precise technique. Obtained results provides an attainable basis for design and interpretation of pQCT studies in children with medical conditions.