Introduction. According to global statistics, secretory otitis media (SOM) ranks first among middle ear infections. This pathology is believed to be characteristic of the pediatric population; however, recent global statistics indicate an increase in the percentage of SOM cases among the adult population. Information about adult-onset SOM varies, with no consensus on the causes of its occurrence. Diverse clinical presentation of the condition, often unsatisfactory treatment outcomes, and a high percentage of recurrences have necessitated a more in-depth study of the etiological factors associated with adult-onset SOM.
 The objective of the research was to determine clinical and morphological parallels in the etiopathogenesis of adult-onset SOM as well as to establish the relationship between the clinical, otoscopic, and endoscopic presentations and pathomorphological changes in the tubal tonsils in these patients.
 Materials and Methods. Sixty-eight (38 men and 30 women) patients with SOM at the age of 18 to 65 years were examined. Fifty-three patients were diagnosed with unilateral pathological process, while in 15 individuals, bilateral SOM was observed. All the patients underwent a comprehensive assessment of their complaints, collection of their medical history, and a full ear, nose, and throat examination using conventional methods, optical techniques, video endoscopy of the nasopharynx and tubal tonsils, and otomicroscopy. In 15 patients, to exclude a malignant process, tissue samples from the tubal tonsils were taken for pathological examination.
 Results. One of the causes of adult-onset SOM could be pathomorphological changes in the tubal tonsils, specifically their inflammation, hypertrophy, and in some cases, tumours. The clinical course and stages of SOM development depend on the duration of auditory tube obstruction. Inflammation of the tubal tonsils usually results in catarrhal and serous SOM, while hypertrophy or hyperplasia of the tubal tonsils is observed in patients with mucous SOM.
 Conclusions. Pathomorphological changes in the tubal tonsils have been established as one of the reasons for developing SOM in adults. Both the clinical presentation of SOM and the stage of its progression depends on the type of pathomorphological changes, their localization (upper or lower pole), and the duration of auditory tube obstruction. A prolonged, recurrent, and treatment-resistant course of SOM may be associated with hypertrophy of the tubal tonsil or tumours. Clinical and morphological parallels identified by us will enable timely utilization of effective etiopathogenetic treatment of SOM and prevent the occurrence of complications.