Non-obstructive azoospermia (NOA) is a form of male infertility caused by disorders of the testicular parenchyma and impaired spermatogenesis. This study aimed to investigate the nature of Leydig cell changes in patients with NOA, especially wether their actual proliferation ocurred. Qualitative histological analysis of the control group of patients (men with obstructive azoospermia and fully preserved morphology of the testicular parenchyma) and biopsies of patients with NOA showed a significant difference in the degree of preservation of spermatogenesis and morphology of Leydig cells. The group of infertile men with NOA Leydig cells sometimes displayed an abundant cytoplasm and were organized into large clusters.