Aim: to identify the clinical laboratory features of coinfection with flu and other respiratory viral infections. Patients and Methods: case records (inpatient files) of 139 children aged 2 months — 18 years who were admitted to Moscow hospitals from October 2017 to February 2020 with the clinical manifestations of acute respiratory infections (ARI) were analyzed. All children were divided into two groups. Group 1 included children with coexisted flu and other ARI (n=31). Group 2 included children with flu alone (n=108). The etiology of ARI was discovered by polymerase chain reaction (oral or nasal smears and/or discharge, sputum) and enzyme immunoassay (antibodies to herpesvirus type 1, 2, and 6, cytomegalovirus, Epstein-Barr virus, Chlamydia, and Mycoplasma). Results: respiratory syncytial virus and rhinovirus were the most common viruses coexisted with flu (8/31 and 5/31, respectively). The onset of ARI occurred 2.60±1.6 days before hospital admission in group 1 and 3.35±1.72 days before hospital admission in group 2 (p>0.05). In group 1, febrile temperature lasted for 4.72±1.25 days that is almost 2 days longer than in group 2 (p<0.01). The rate of complications in coinfection with flu and ARI vs. flu alone was different, i.e., acute (catarrhal, medium) otitis was diagnosed in 35.5% and 8.3.% (p<0.01), respectively, acute sinusitis in 12.9% and 8.3%, respectively, and pneumonia in 22.6% and 7.4%, respectively. Conclusion: in children, coinfection with flu and other respiratory virus is generally more severe as demonstrated by higher temperature, more severe intoxication symptoms, more common complications (e.g., otitis, sinusitis, pneumonia etc.), and a greater need in infusion therapy. Co-infected children are admitted to hospital more rapidly and stay in hospital for a longer period. KEYWORDS: acute respiratory infections, flu, rhinovirus, children, fever, intoxication, severity. FOR CITATION: Nikolaeva S.V., Usenko D.V., Shabalina S.V. et al. Clinical presentation of flu coinfections in children. Russian Medical Inquiry. 2020;4(11):665–669. DOI: 10.32364/2587-6821-2020-4-11-665-669.