Chlamydia pneumoniae is one of the common pathogens in community-acquired pneumonia (CAP). The clinical presentation is usually mild or even unrecognized. Severe CAP due to C. pneumoniae is usually found in the elderly or in patients with underlying diseases. Herein, we report a previously healthy young adult, who developed severe CAP with rapid progression to acute respiratory distress syndrome (ARDS) due to C. pneumoniae infection. With aggressive treatment, the patient recovered well without residual pulmonary function impairment. If a patient presents with ARDS without a clear-cut etiology, C. pneumoniae infection should be included in the differential diagnosis, even in the healthy young adult.