An increased risk of testicular cancer in men with infertility and poor semen quality has been reported. In view of the high cure rates for testicular germ cell tumours, increasing clinical importance is being placed on the protection of fertility. High-dose cytostatic therapy may be expected to cause long-term infertility. Thus, the standard procedure for fertility protection is the cryopreservation of ejaculated spermatozoa or testicular tissue before therapy. Four male patients with azoospermia and two patients with very severe oligozoospermia underwent onco-testicular sperm extraction (TESE). We attempted onco-TESE in patients with azoospermia and very severe oligozoospermia after orchiectomy. Of the patients with testicular germ cell tumours, four had spermatozoa in their testicular tissues. Sertoli cell-only syndrome was found in one patient, and one patient showed maturation arrest without the detection of spermatozoa. Three of six showed seminomatous germ cell tumour, two of six had nonseminomatous germ cell tumour and one patient showed no malignancy. Two patients achieved clinical pregnancy. Fertility challenges in men with cancer are the most straightforward because of the relative ease of obtaining and cryopreserving sperm. Testicular sperm extraction is a useful technique for obtaining spermatozoa before cytotoxic therapy in azoospermic and very severely oligozoospermic cancer patients.