Abstract Objective To evaluate the expression of type IV collagen [α1(IV) to α6(IV)] in testes and the association with spermatogenesis. Design Retrospective immunohistochemical study. Setting Division of Urology, Department of Organs Therapeutics, Faculty of Medicine, in a university hospital. Patient(s) Testicular biopsy specimens were obtained from 24 patients with varicocele, 5 with Sertoli cell-only syndrome (SCO), and 5 normal volunteers. Intervention(s) Collection of testicular tissue and blood and semen sampling. Main outcome measure(s) Expression of type IV collagen subtypes assessed by immunohistochemistry and clinical parameters such as seminogram and hormonal findings. Result(s) In normal testes, the α1(IV) chain was seen in the basement membrane (BM) of seminiferous tubules as strongly stained irregular, wavy double lines, and the α2(IV) chain was slightly detected, whereas other testes showed little staining. In patients with varicocele and Sertoli cell-only syndrome, the BM was thicker and α1(IV) and α2(IV) chains were stained more intensely in the BM of seminiferous tubules than in normal testes. The expression of α1(IV) chain, not α2(IV), significantly correlated positively with the BM thickness, and negatively with sperm concentration, tubular diameter, and Johnsen score. Conclusion(s) Overabundance of the α1(IV) chain is associated with increased BM thickness and possibly related to spermatogenic dysfunction.