Patients with a prior history of a germ cell tumor of the testicle are known to have an increased risk of development of a second germ cell tumor in the contralateral testicle. It is believed that all patients who develop a germ cell tumor of the testicle have a precursor lesion know as carcinoma in situ (CIS) or intratubular germ cell neoplasia. Approximately 50% of these patients will subsequently go on to develop a germ cell tumor in the testicle. A biopsy of the contralateral testicle in a patient with a previous history of a germ cell tumor of the testicle has been advocated by some, while others recommend a biopsy only in patients with other risk factors as well. The arguments for biopsy are that intervention may be used to prevent the development of a second germ cell tumor when CIS is detected. In this review we present the arguments for and against a biopsy of the contralateral testicle, review the techniques of biopsy as well as its complications, and discuss the interventions employed to prevent CIS from progressing.