Individuals with Down syndrome (DS) have a predisposition to leukaemia and testicular cancer, but data on the incidence of cancers are yet sparse. A cohort of 3,581 persons with DS was identified from a National Registry of Finnish persons with intellectual disability collected between 1978 and 1986 and followed‐up for cancer incidence until 2002. Standardised incidence ratios (SIRs) were defined as ratios of observed number of cancer cases to those expected from the national cancer incidence rates, by age and sex. The overall cancer risk was equal to that of the general population, but a significantly high risk of leukaemia (SIR 10.5, CI 95% 6.6–15.8) and testicular cancer (SIR4.8, CI 95% 1.8–10.4) was found. © 2005 Wiley‐Liss, Inc.