Background: LDH (lactate dehydrogenase), AFP (alpha-fetoprotein) and beta-HCG (human chorionic gonadotropin) are used in diagnosis and follow-up of testicular germ cell cancer (TGCC) patients. Our aim was to investigate the association between levels of miR-371a-3p, miR-373-3p and miR-367-3p and clinical features in metastatic TGCC. Methods: relative levels of miR-371a-3p, miR-373-3p and miR-367-3p were evaluated in serum of metastatic TGCC patients. A prospectively included and a retrospectively selected cohort were studied (total patient number = 109). Blood samples were drawn at start of chemotherapy and during follow-up. Serum microRNA (miR) levels were determined using the ampTSmiR test. Results: at start of chemotherapy, miR-371a-3p, miR-373-3p and miR-367-3p levels were positively correlated to LDH. The median level of these miRs was higher in patients who developed a relapse after complete biochemical remission (n = 34) than in those who had complete durable remission (n = 60). Higher levels of miR-367-3p were found in patients with refractory disease (n = 15) compared to those who had complete response. miR levels decreased during the first week of chemotherapy in patients with complete response and stayed below threshold after one year of treatment. Conclusion: high miR levels at start of chemotherapy are associated with worse clinical outcome and can assist in early diagnosing of relapses.