The article describes a method that can predict nasal mucosal infection in patients with chronic rhinitis and paranasal sinusitis, without using laboratory tests. The method is based on the determination of an integral Chlamydia infection risk index that is calculated from clinical and anamnestic rating scale scores. The proposed method was tested in 201 patients with an exacerbation of chronic maxillary sinusitis who were examined for Chlamydophila pneumoniaе and Chlamydia trachomatis. The most significant advantages of the method were to improve the efficiency of clinical diagnosis of Chlamydia infection, to purposefully select patients for the expensive laboratory verification of Chlamydia, and to perform timely anti-Chlamydia treatment assisting in declining the number of complications and in preventing the dissemination of the infection. The high operational characteristics of its clinical and anamnestic diagnosis determine the expediency of its use by a wide range of medical specialists (ENT doctors, therapists, pediatricians, infectiologists, and general practitioners) in the out- and inpatient care facilities.