Acute tumour lysis syndrome (TLS), a condition resulting from rapid destruction of tumour cells with massive release of cellular breakdown products, has been described following the treatment of various malignancies. However, spontaneous TLS has been described only rarely. Germ cell tumours (GCT) have a rapid cell turnover and often present with bulky metastatic disease. We report two cases of patients with metastatic GCT presenting with acute renal failure attributable to spontaneous TLS. All clinical and biochemical features of the syndrome were present. Both patients were treated with haemodialysis and intravenous administration of single-agent etoposide between dialysis sessions, resulting in recovery of renal function and marked decrease in tumour bulk within the first week after presentation. These cases are the first reported instances of spontaneous TLS in poor-risk metastatic GCT. Successful treatment with dialysis and chemotherapy is possible, and prophylactic vigorous hydration and allopurinol may be warranted in this setting.