Background. The study of the structure and mechanogenesis of falls is necessary to elucidate causal relationships in criminal catatrauma. Purpose of the study was to analyze the structure of mechanical injury resulting in fractures of the long bones of the lower extremities, and the mechanisms of their formation in victims as a result of a fall, according to the primary forensic examination. Material and methods. The study was carried out based on 130 reports of primary forensic examinations of victims with fractures of the femur and / or shin bones due to mechanical injury for the period February – June 2018. All victims were divided into 4 groups: group 1 included individuals sustaining mechanical injury; group 2 involved individuals sustaining injuries in car accidents; group 3 included patients with traumas from the fall, and group 4 included individuals with gunshot fractures. The methodology of the study was based on applying retrospective analysis, descriptive statistics. Results. In cases of catatrauma, the proportion of fractures of the lower extremities makes up 52%, while the proportions of fractures of the upper limbs, ribs and pelvic bones constitute 16% each; in case of car accident the fractures of low legs make up 82.1%, while the fractures of the upper limbs, ribs and pelvic bones constitute 7.8%; 2.4% and 7.7% each, respectively. There are two types of catatrauma included found out in this study: 1) household falls from the own body height (n = 4), and 2) falls from the height not exceeding 3 m (n = 9). The catatrauma mechanisms included the following: 1) active free uncoordinated fall from the own body height with the phase of primary collision with some isolated primary direct injuries; 2) passive free direct predominantly uncoordinated fall from a height of up to 3 m resulting in multiple combined injuries in the phase of primary collision (n = 4), and in the phases of primary and secondary collision of the body (n = 3). Conclusions. In the structure of mechanical injuries of the long bones in the lower extremities according to the initial forensic medical examination, falls from various heights rank the second position among the most frequent criminal injury (10%) after road traffic injuries (89,2%). Falls from own body height and from the height of up to 3 m were free, straight, and mostly uncoordinated, resulted in mainly primary direct injuries as the fractures of the long bones of the upper and lower limbs, ribs, pelvis, brain concussion, chest bruises and abdominal traumas.