Testicular germ cell tumours (GCTs) are the most common malignancy among young men. Management of GCTs relies on the serum tumour markers α-fetoprotein, human chorionic gonadotropin, and lactate dehydrogenase, among other parameters. However, these tumour markers can only be detected at elevated levels in half of GCT patients. Circulating miR-371a-3p has emerged as a blood-based biomarker that can reliably detect macroscopic GCTs, aside from teratoma. Here we review the literature, describe the methodologies currently used to measure circulating miR-371a-3p, and discuss the following clinical scenarios in which miR-371a-3p may impact practice in the future: (1) men with an inconclusive small testicular mass; (2) response monitoring during chemotherapy; (3) postchemotherapy residual masses; and (4) follow-up after treatment with curative intent. PATIENT SUMMARY: We discuss the potential uses and promise, as well as current limitations, of a novel blood test that may improve care for men with testicular cancer.