Mycoplasma pneumoniae infection is typically a disease of otherwise healthy adolescents and adults and is a common pathogen in this population. Approximately 20% of infections are asymptomatic. The majority of symptomatic infections present as mild upper respiratory tract infections or tracheobronchitis. Only 5% of infections result in pneumonia. The usual clinical symptoms include fever, sore throat, cough, chills, headache, and malaise. The symptoms are often disproportionately compared to the radiologic findings. Few cases are biopsied. Acute bronchiolitis may be seen. Mycoplasma is in the differential diagnosis of organizing pneumonia formerly known as bronchiolitis obliterans organizing pneumonia (BOOP).