Testicular germ cell tumours have a favourable prognosis if detected early, but are potentially lethal in a subset of patients. Multi-modality treatment is often necessary, thus the preferable time of diagnosis is at the pre-invasive, but unfortunately often asymptomatic precursor stage of carcinoma in situ (CIS). This review describes current possible approaches for the detection of CIS. At present, an open testicular biopsy is the only definitive way of establishing the presence of CIS. The tissue section should be of an adequate size, be properly fixed, and evaluation be supported by at least one solid immunohistochemical marker, for example PLAP, OCT-3/4 or AP-2gamma. Determination of who should be offered testicular biopsies is based on clinical and ultrasonic examination along with the evaluation of risk factors. A surgical biopsy is an invasive procedure with potential complications, although rare. Therefore, a noninvasive and equally reliable method is needed. Testicular ultrasound is risk-free, painless and at present the only noninvasive method of aid for andrologists when CIS is suspected. The presence of testicular microlithiasis is, in some cases, indicative of pre-malignant changes, especially in males with additional risk factors. Promising results have recently been obtained with a novel noninvasive detection method based on immunocytological AP-2gamma-staining of CIS cells in semen. This method could be a supporting method in andrology centres where careful follow-up is possible. In conclusion, one difficulty is to determine in which males CIS should be suspected; secondly, there does not as yet exist an optimal noninvasive method of diagnosis that is more acceptable than an open surgical biopsy.