Pre-school period is a period of intensive psycho-physical development of children, as well as the time of shaping nutritional habits and taste preferences. The objective of the study is the assessment of the BMI index and body mass components in a selected group of pre-school children, and the analysis of the relationship between their nutritional mode and the contents of fatty tissue in the body. The study covers 324 children from randomly selected nursery schools in Cracow. Normal weight-height propportion was observed in 83% from among 324 children covered by the study. Underweight was noted in 10.8% of children, while 6.2% were overweight or obese. In 74 children, who had body mass components determined, the percentage of fatty tissue was 15.8%+2.9% on average. The content of fatty tissue in children aged 7.5 years was higher by 3.1%, compared to those aged 4.5 years. The mean caloric value of the diet was 1982.80 + 580.84 kcal. Body mass deficiency concerned a higher percentage of children than the excess, considering overweight and obesity jointly (10.8% vs. 6.2%). The relationship between the content of fatty tissue and caloric value of the diet among pre- school children was difficult to evaluate due to the lack of the reliability of parents while reporting/assessing the menu of their children.