Introduction. Juvenile idiopathic arthritis (JIA) is a common multifactorial disease characterized by the presence of chronic inflammation in the joints, entheses and other structures of the musculoskeletal system in combination with a certain range of extraskeletal disorders. Vast variety of JIA clinical variants and the variability of the disease course make primary and differential diagnosis difficult, which often leads to a delayed start of treatment and an inadequate choice of medical therapy or, conversely, an excess of medication. In the range of differential diagnostic conditions that have similar symptoms and are manifested by severe arthralgia, gait disturbance, joint stiffness, as well as the presence of effusion and gradual progression of bone destruction mainly in the epiphyseal plate, one should remember about hereditary skeletal dysplasias, primarily from a genetically heterogeneous group of multiple epiphyseal dysplasias (MED). The aim of the study – description of the clinical and genetic characteristics of three patients with various genetic variants of MED and defining approaches for their differential diagnosis with JIA. Materials and methods. There were three patients from three unrelated families aged from 7 to 13 years old under our supervision. To clarify the diagnosis, a genealogical analysis, a clinical examination of patients and first-degree relatives, as well as an assessment of X-ray images of long tubular bones were carried out. Molecular genetic confirmation of the MED diagnosis types 1 and 2 was based on the results of custom panel sequencing consisting of 166 genes responsible for the development of hereditary skeletal pathology. To clarify the molecular genetic diagnosis of MED type 4, an analysis of the SLC26A2 gene was performed using automated Sanger sequencing. Results. Anamnestic, clinical, radiological, and molecular genetic characteristics of three unrelated patients with different genetic types of MED caused by variants in the COMP, SLC26A2, and COL9A2 genes were analyzed. The first symptoms of the disease in observed patients with three different genetic variants of MED occurred at the age of 2–3 years old and were characterized by gait disturbance and climbing stairs difficulties. Gradually, these symptoms were accompanied by pain in large joints. According to the ultrasound examination of the joints, signs of synovitis were noted, as a result they were diagnosed with JIA (polyarticular variant, seronegative for rheumatoid and antinuclear factor) and immunosuppressive therapy were prescribed without significant effect. The atypical course of the JIA was the reason for additional examination of patients by an orthopedist and geneticist. Careful analysis of the large joints radiographs made it possible to suspect one of the variants of MED in our patients based on the detection of distinctive signs, which were characterized by abnormal ossification (diminished size and flattening) of the epiphyses and abnormal shape and structure of the femoral head epiphysis. Molecular genetic analysis was performed to confirm the diagnosis. As a result, a pathogenic variant of the nucleotide sequence in the COMP gene was detected in one of the patients, two pathogenic variants in the SLC26A2 gene in another patient, and one pathogenic variant in the COL9A2 gene in the third patient, which made it possible to confirm the final diagnosis of MED type 1 with an autosomal dominant type of inheritance, MED type 4 with an autosomal recessive type of inheritance and MED type 2 with an autosomal dominant type of inheritance, respectively. Based on the results of our own research and analysis of the literature data, key directions for the differential diagnosis of MED and JIA were formulated. It is shown that the analysis of the X-ray images of patients is essential in differential diagnosis. Conclusion. Despite the significant overlap of the clinical symptoms between JIA and MED, the key to the early diagnosis of MED is a comprehensive examination, which included genealogical analysis, features of clinical manifestations and disease course in combination with distinctive radiological signs including delayed ossification of the epiphyses of tubular bones typical for MED. However, the question remains about the probability of a combined nature of osteoarticular disorders, i. e., the possible development of JIA in patients with hereditary skeletal dysplasias which requires in-depth study in the future.