An increased number of patients with syphilis was recently reported in Japan and the United States. Syphilitic orchitis, a late complication of syphilis, is a rare disease that presents as testicular swelling. In most cases, a diagnostic orchiectomy is performed because of the possibility of testicular cancer. We report a case treated conservatively with antibiotics considering the possibility of syphilitic orchitis based on the blood test results and describe long-term changes observed in the imaging findings.