A case of testicular dermoid cyst in a 19-year-old adult who was presented for evaluation of a presumed testicular neoplasm is reported. Ultrasonography and pelvic computerized tomography (CT) were performed for differentiation of benign or malignant lesion. Testicular tumor markers were negative. Simple inguinal orchiectomy was performed and the dermoid cyst was confirmed pathologically. We discuss the pathogenesis, diagnosis, and treatment. (J Urol R.O.C., 8:168-170,1997)