Introduction The prevalence of excessive and insufficient body mass in children is increasing worldwide according to epidemiologic researches. There is a risk of health disorder with the fluctuation of body mass.

Aim To determine the current situation in Latvia, estimate the amount of thin and overweight children and calculate Fat Mass Index using the skin fold measurements.

Methods 1025 Latvian youngest grade schoolchildren were selected from 2007 to 2009 and a cross sectional survey carried out using questionnaire and anthropometric methods as well as somatotype analysis. The percentage of body fat was estimated using the sum of two skin folds. Fat mass index (FMI), FFMI (Fat Free Mass Index) and Body Mass Index (BMI) were calculated accordingly. Children were divided into groups to determine the nutrition level using 3rd, 15th, 85th and 97th BMI and FMI percentile values.

Results The results show that the amount of children with extremely low body mass is equally significant with those with adiposity diagnosed using BMI. When using BMI to analyse the changes, children with normal fat percentages show decreased, normal and increased body mass values.

Conclusions Significant numbers of children have a low or critically decreased body fat mass. This problem is very vital and has to be evaluated as a highly dangerous risk factor for health and prospective life quality of the children. It is recommended to use FMI when analysing changes in body mass. Hyperdiagnosics of adiposity occurs when BMI is used.