To assess the effect of experimental Type 1 diabetes on male fertility, male Sprague Dawley rats were injected with either streptozotocine (STZ) to induce diabetes or with citrate buffer as controls. Diabetic animals and 2 control groups (STZ-resistant and buffer-injected rats) were sacrificed at 2 different times after injection: 6 weeks (6W) and 20 weeks (20W). We analyzed serum testosterone (sTT), epididymal sperm parameters, and weight of testicles and epididymides, and carried out a histological evaluation of testicular tissue. Diabetic animals presented a significant increase in teratozoospermia (20W, P , .01) and a decrease in sTT (P , .01), tubular diameter (6W, P , .05), and testicular (6W, P , .01) and epididymal (P , .01) weight. STZ-resistant animals showed significantly decreased sTT (6W, P , .01), epididymal weight (6W, P , .05), and sperm count (6W, P , .01) compared with bufferinjected controls. Experimental STZ diabetes increases teratozoospermia and decreases sTT, testicular weight (reverting at mediumterm), and epididymal weight.