BACKGROUND: FDG-PET is a diagnostic imaging procedure effective in staging primary and recurrent cancer. False-positive uptake already has been described in both inflammatory and infectious respiratory diseases, although no reports associate Chlamydia pneumoniae infection to FDG uptake. CASE REPORT: An incidental diagnosis of asymptomatic multilobar pneumonia during screening for thyroid malignancy is reported. Three areas of pulmonary consolidation strongly positive on PET/CT scan, mimicking pulmonary malignancy were identified. Both radiologic features and serum IgM antibodies for Chlamydia pneumoniae suggested the diagnosis of an unusual presentation of a Chlamydia pneumoniae respiratory infection. Specific antibiotic therapy induced a complete resolution of the areas of pulmonary consolidation. CONCLUSIONS: This case suggests that positive PET is not an absolute indicator for malignancy. Chlamydia pneumoniae respiratory infections can exhibit positive uptake on FDG-PET.