Mycoplasma pneumoniae is a common cause of respiratory infections in children and adults, but the most severe presentations tend to be in older children and adolescents. The organism causes up to 30% of primary atypical pneumonia (PAP), but it is now recognized that these severe manifestations of infection represent only a small percentage of respiratory infections due to this species of bacteria. Typical incubation times until the development of symptoms are remarkably slow for a bacterial infection, usually between 2 and 3 weeks. The typical presentation includes flulike symptoms with cough, often with sore throat, headache, malaise, and fever. Symptoms, particularly cough, may be very prolonged despite appropriate antibiotic therapy, sometimes lasting up to 3 months. Cough, initially dry, may become productive of purulent sputum as the illness progresses. Examination of the throat may reveal some erythema but usually no exudates or associated lymphadenopathy. Auscultation of the chest in patients with PAP often demonstrates fine inspiratory rales, particularly at the lung bases, and occasionally expiratory wheezing. Chest films may show streaky unilateral or bibasilar infiltrates, peribronchial thickening, and not infrequently small pleural effusions. Computed tomographs of the chest are very likely to show peribronchial thickening and centrilobular nodules with a tree-in-bud pattern and patchy areas of airspace consolidation. Accurate diagnosis of M. pneumoniae infections is complicated by a current lack of rapid diagnostic techniques with appropriate sensitivity and specificity. © 2013 Bentham Science Publishers.