Long term use of topical vasoconstrictors for the nose may result in rhinitis medicamentosa, the rebound swelling of the nasal mucosa. Usually discovery of any underlying reason for decongestant use is impossible, therefore treatment could be problematic. The aim of this study was to establish the nasal mucosal cytology of patients with rhinitis medicamentosa and evaluation of usefulness of exfoliative cytology in diagnostics of underlying reason of nasal decongestants overuse. All patients had a history of six months regular use of popular intranasal alpha-adrenomimetics. All patients have used them constantly with different frequency in 24 h, but always before sleep. The exfoliative cytology was used as a method of nasal mucosa evaluation. Normal cytograms in rhinitis medicamentosa were in 16.4%. Cytograms of 13.4% patients showed a significant number of eosinophils and 29.9% predominant of squamous metaplasia. The study showed that the majority of cytograms in rhinitis medicamentosa indicates nasal mucosa injury. Method of the exfoliative cytology could facilitate the establishment of the underlying cause of intranasal decongestants overuse.