RESUMEN
<p><b>OBJECTIVE</b>To report a rare case of ectopic mesonephric duct cyst with ectopic testicular malignancy and improve the diagnosis and treatment of the disease.</p><p><b>METHODS</b>We retrospectively analyzed the clinical data of a case of ectopic mesonephric duct cyst with ectopic testicular malignancy, reviewed relevant literature at home and abroad, and investigated the pathogenesis, diagnosis and treatment of the disease.</p><p><b>RESULTS</b>A large cyst and the right ectopic malignant testis were removed via abdominal incision, and the left undescended testis was lowered into the scrotum. Pathological examination confirmed the lesion to be right ectopic mesonephric duct cyst with right ectopic testicular seminoma. No metastasis was found during a year of follow-up.</p><p><b>CONCLUSION</b>Ectopic mesonephric duct cyst with ectopic testicular malignancy was a rare disease. Imaging examination contributes to its diagnosis, but it has to be confirmed by pathology. Surgical removal should be performed as early as possible and follow-up treatment depends on the pathologic type and stage of ectopic testicular malignancy.</p>