Summary: There has been great progress in the understanding of the molecular events involved in normal germ cell maturation and testicular tumour pathobiology. Identification of the molecules involved in these processes has provided a number of new immunohistochemical markers for intratubular germ cell neoplasia, unclassified (IGCNU) and germ cell tumours. OCT4, the most important of the newer markers, is highly sensitive and specific for IGCNU and is superior to older immunohistochemical markers for this purpose. However, germ cell maturation delay is a potential pitfall in the application of this marker. In contrast to the type II testicular germ cell tumours, relatively little is known about premalignant lesions of testicular sex cord–stromal tumours, malignancies of the rete testis and epididymis, and paratesticular malignancies.