Objective: Lower respiratory tract infections are one of the major causes of morbidity and mortality in children worldwide. Besides, epidemiological data on this subject is very limited. Mycoplasma pneumoniae is an important bacterial agent in community-acquired pneumonia (CAP) and may cause mild, moderate and severe lower respiratory tract infections. Clinical diagnosis is very difficult. Material and Methods: In this study, it was aimed to determine the seroprevalence of M. pneumoniae in children aged 0-17 years admitted to a medical faculty in Istanbul with lower respiratory tract complaints or non-respiratory findings such as cytopenia and arthritis/arthralgia and to determine the prevalence of infection among children in various age groups. One hundred and thirty-four patients were included in the present study. Venous blood and nasopharyngeal swab samples were taken from study patients. M. pneumoniae IgG and IgM antibodies were determined by ELISA (Enzyme Liquid Immunoassay) test in blood samples and M. pneumoniae Real-time polymerase chain reaction (RT-PCR) test was performed in nasopharengeal swab samples. Results: Seropositivity was seen in 50 (37.3%) patients, only specific IgM antibody positivity in 5 (3.7%) patients, both specific IgM antibody and specific IgG antibody positivity in 8 (6%) patients and 37 (27.6%) patients specific IgG antibody was also observed. The number of M. pneumoniae DNA RT-PCR positive samples was shown to be only 2 (1.5%), both of which were not serologically positive. Conclusion: Our results show a significant prevalence of M. pneumoniae in children diagnosed with acute respiratory infection. It also highlight the importance of laboratory detection for appropriate and rapid antibiotic treatment.