Primary malignant mediastinal germ cell tumours are rare and considered to have poorer prognosis compared with those arising from gonads. Eighteen patients with primary mediastinal germ cell tumour were treated over an 1-year period; 9 had seminoma and 9 non-seminoma. Eight patients, 4 each with seminoma and non-seminoma underwent initial tumour excision and the rest had biopsy only. All patients received cisplatin-based chemotherapy. All patients with seminoma received consolidation radiotherapy to mediastinum. Three patients with non-seminoma received radiotherapy following partial response. All 9 patients with seminoma achieved complete response at the end of chemotherapy. Two patients with NSGCT had complete response to chemotherapy, 5 partial response and 2 no response. Two patients who underwent resection of the residual tumour mass are surviving free of disease. Addition of radiotherapy or second-line chemotherapy did not bring about any added response in partial and non-responders. Nine out of 9 patients with seminoma and 4/9 with non-seminoma are surviving disease-free at a median follow-up of 48 months (range 16 153 months). Mediastinal seminoma has excellent prognosis with cisplatin combination chemotherapy, whereas non-seminoma carries poor prognosis, and aggressive chemotherapy with resection of residual masses may improve the outcome. The role of additional radiotherapy and initial tumour debulking needs further evaluation.