Retinoblastoma is a rare tumour. The gene involved in the formation of retinoblastoma has been identified, and it has since been shown to be implicated in many other tumour types. In addition, patients with the familial form of retinoblastoma are known to be at an increased risk of developing second primary, non-ocular, malignancies. Retinoblastoma provides us with an important insight into the genetic mechanisms involved in tumorigenesis, to the extent that the retinoblastoma gene has now become the archetype of the 'tumour-suppressor' genes. The importance of this class of genes in tumorigenesis may come to exceed that of the oncogenes.