An experimental study was planned to evaluate if contralateral testicular deterioration following ipsilateral torsion requires the presence of a twisted ipsilateral testis and/or epididymis. Five groups, each containing 6 rats, were established. The groups underwent sham operation, epididymo-orchiectomy, testicular torsion, torsion following subepididymal orchiectomy and torsion following epididymo-orchiectomy. After 24 h, the contralateral testes were harvested and the percentage of haploid cells was determined by DNA flow cytometry. Ipsilateral torsion, in the presence and absence of testis and epididymis, significantly decreased the number of haploid cells compared to sham and epididymo-orchiectomy procedures. Torsion of only the ipsilateral spermatic cord and adjacent vasculature seemed to suffice to damage the contralateral testis. Since the presence of the ipsilateral testis and epididymis is not mandatory for this acquired damage, which occurs within 24 h, a role for a preexisting congenital defect and autoimmunity seems unlikely.