The aim of this study was to determine whether the living conditions of school children affects their body structure and muscular strength. Data were taken from 400 girls and 341 boys aged 7–15 years attending nine primary schools in Warsaw in 1997. A questionnaire was completed, anthropological measurements made and two muscular strength tests conducted. The questionnaire asked questions on the children’s level of education, their parents’ professions and monthly incomes, the number of persons in the family and the number of rooms in the family’s apartment/home. Body height, body weight, chest and arm circumferences, grip strength and vertical jump height were measured and used to calculate body mass index, Marty’s Index and the Sargent Vertical Jump Index. Statistical tests included Student’s t-test, Principal Component Analysis (PCA) and multiple regression analysis. Body height, chest circumference, Sargent Vertical Jump Index and grip strength were significantly greater in the boys than the girls. Two factors, namely ‘socioeconomic status’ (F1) and ‘family size’ (F2), describing living conditions, were isolated after PCA. Boys from bigger families (F2) were shorter, with lower weights and BMIs, smaller chest and arm circumferences and greater grip strengths than those from smaller families, whereas girls from families of lower socioeconomic status (F1) weighed less and had greater BMIs and arm circumferences than those from higher socioeconomic status families. The results suggest that boys seem to be more ‘ecosensitive’ than girls.