Nowadays, male and female infertility factors can cause infertile marriage with the same frequency. It is known that the causes of male infertility can be varicocele, genetic disorders, endocrine diseases, congenital pathologies, injuries and inflammatory diseases. Despite a sufficient set of diagnostic techniques, the form of male infertility remains unidentified (idiopathic) in 1/3 of men. At present, the role of mast cells (MC) in the development of chronic pelvic pain syndrome, chronic prostatitis, and chronic epididymitis are shown. However, the role of MC in the formation of male infertility still remains open. The article presents a clinical case of a male patient with primary infertility and non-obstructive azoospermia, who underwent a testicular biopsy to identify the causes of infertility. Morphological examination of the biopsy specimen revealed the MC population in the testicular interstitium. This particular finding allows to explain the presence of fibrosis in the connective tissue and the epithelium of convoluted seminiferous tubules in this patient. The revealed testicular fibrosis led to a permeability disorder of the blood-testis barrier and a spermatogenic epithelial cell death, resulted in the development of azoospermia in the particular male patient. © 2022, Meditsina-Inform LLC. All rights reserved.