Background: Contemporary anthropological research confirms the fact that body composition is one of the elements differentiating athletes from persons not practising sport systematically. The differences in body composition - in many cases even extreme - also regard athletes in the context of the sports discipline they practise.The aim of the study was to determine the properties of body composition of the Polish national team pentathletes in comparison to persons of the same population not practising competitive sport.Material/Methods: The research comprised members of the Polish national team in modern pentathlon (n=10). The subjects were 18-23 (20±1.5) years of age with their body mass from 64 to 80 kg (73.27±6.1) and body height of 172-188 cm (180.11±6.22). The athletes had had 6-13 years (10.38±2.07) of training experience. Students of Warsaw Technical University (Poland) constituted the reference group. Measurements of 20 basic somatic features were made. The following indices were calculated: leanness, Rohrer's, BMI, Manouvrier's and pelvic-shoulder. Body density, total body fat, active tissue, the general body composition profile and internal proportions of the body composition were determined.Results: An analysis of internal proportions of the factors of athletes' body composition revealed differences in particular groups of features. The athletes' overall body size results from greater than mean values of the body height and the average ones of stoutness and the fat content.Conclusions: The proportions of features within the analysed factors proved a significant advantage of the upper limb over the lower one and the significant predominance of the musculature of the forearm.