Reliable risk figures are available for regular trisomy G cases and the more common translocation types. In trisomic Down’s syndrome risk figures depend on maternal age. In the maternal age group below 30 the available materials lead to an estimated risk of recurrence of 1–2%. In translocation cases the risk depends on the type of translocation and the sex of the carrier. In (DqGq) translocations, risk figures of about 10% have been estimated for female carriers. Nearly the same risk was obtained for females with (21q22q) translocation. For male carriers the risk could not be estimated separately, but it is considered to be small (at most a few per cent). More research is needed concerning the role which chromosomal variation and other chromosomal abnormalities may play in the origin of Down’s syndrome.