The differences in human motor development are determined by predispositions and living conditions. The aim of the present study was to examine relationships between motor fitness of children and adolescents aged 8-16 years (277 boys and 247 girls), and their somatic build and quality of life of their families. Body height, body mass and skinfold thickness were measured. On the basis of these measurements body mass index (BMI), Rohrer's index and lean body mass (LBM) were calculated. The subjects' physical fitness was also assessed with motor tests: speed of arm movement (plate tapping), agility (10 × 5 m shuttle run), explosive strength of the legs (standing broad jump), trunk strength (situps), explosive strength of the trunk and shoulder girdle (1-kg medicine ball throw), and flexibility (sit and reach) regarded as a morpho-functional predisposition of motor abilities. The standing broad jump results were then used to calculate maximal anaerobic power (MPA). The examination was completed with a questionnaire survey of the children's parents concerning their families' quality of life. On the basis of the parents' answers to the questionnaire, two quality of life indices were constructed: objective quality of life index and subjective quality of life index. Due to the wide age bracket of subjects the sample was divided into two age groups: 8-12 and 13-16-year-olds. The relationships between subjects' motor development, somatic traits and their families' quality of life were examined with the use of multivariate comparative analysis. The level of motor development of studied children was more strongly determined by their somatic build than the quality of life of their families. The most important somatic determinants of the subjects' motor abilities were body height and subcutaneous adiposity. These determinants primarily affected speed and strength abilities of younger school children. Objective quality of life of children's families determined the development of some strength abilities in children aged 8-12 years. No correlations between the subjects' motor development and subjective quality of life of their families were found.