There are relatively few studies on the association between environmental tobacco smoke (ETS) during pregnancy and childhood, and cancer in childhood, adolescence or adulthood. The associations between maternal smoking during pregnancy and childhood cancer have been studied intensively, but there is no clear association overall, or for specific sites. The association between childhood cancer and smoking by the father in the preconceptional period, and by either parent during the child's lifetime, has been little studied. Again, no clear associations have been identified. However, evidence from studies of exposure to known carcinogens from ETS, and of genotoxic effects indicates that any effect, if present, is expected to be weak, and therefore could not have been detected by most of the studies which have been performed, due to the small number of cases included. There is some consistency of association between ETS exposure in childhood and the risk of lung cancers in adulthood. There is therefore a need for further epidemiological studies on ETS exposure during pregnancy and childhood and the occurrence of cancers.