Introduction. Chronic recurrent cystitis (CRC), notwithstanding the advancements of up-to-date uroinfectology, remains an urgent and controversial problem. An important section of this issue is the study of the etiology of the disease, the determination of which defines the success of treatment and the planned scope of prophylaxis.
Objective. To study pathomorphological changes in the bladder urothelium of patients with chronic recurrent cystitis depending on the etiological factor.
Materials and methods. One hundred fifty eight sexually active female patients aged 20–45 years who had previously been diagnosed with recurrent lower urinary tract infection / chronic recurrent cystitis (RLUTI / CRC) during exacerbation were included in this prospective study. Based on the results of bacteriological and PCR studies of urine, urethral and vaginal discharge, patients were divided into four groups depending on the dominant etiological factor (bacteria / HPV / Candida spp. / M. tuberculosis). Bladder biopsy was performed in remission stage of the disease after premedication and general anaesthesia as routine during cystoscopy. Biopsy specimens after standard preparation were subjected to histological study with characterisation of the changes.
Results. The histological study results revealed characteristic specific pathomorphological tissue changes in different groups, which allowed us to define a protocol for differential diagnosis of RLUTI.
Conclusions. One of the guiding methods of differential diagnostics of RINMP / CRC defining the genesis of infectious-inflammatory process in the bladder is histological study of its biopsy specimens.

Keywords: human papillomavirus viruses, Candida, Mycobacterium, biopsy, recurrent cystitis, bacteria