Currently, there is a nationwide outbreak of Mycoplasma pneumoniae infections. M. pneumoniae is a bacterium that can cause atypical pneumonia, especially in children and young adults, and does not respond to the standard antibiotics prescribed for pneumonia. In addition, the bacterium regularly causes extra-pulmonary symptoms. In our hospitals, we have admitted 100 patients (including 20 children) with M. pneumoniae since the fall of 2023, many of which were young and had severe clinical symptoms. It is important to recognize the clinical picture to start effective antibiotic treatment. In this clinical lesson, we will provide two examples of recently admitted patients and discuss the characteristics of all inpatients who have presented to our hospitals during this epidemic. Finally, we pay attention to antibiotic policy and antibiotic resistance.