The aim of the present study was to address the unresolved question of the risk of neoplasms among people with intellectual disability (ID). A total of 2173 individuals with ID from a large, representative, nation-wide population study conducted in Finland in 1962 were followed-up for cancer incidence between 1967 and 1997. Standardized incidence ratios (SIRs) were defined as ratios of observed to expected numbers of cancer cases. Expected rates were based on national incidence rates. The observed number of cancers in the cohort (173) was close to what was expected [SIR = 0.9, 95% confidence interval (95% CI) = 0.8-1.0]. There was a significantly reduced risk of cancers of the prostate (SIR = 0.2, 95% CI = 0.0-0.5), urinary tract (SIR = 0.3, 95% CI = 0.1-0.7) and lung (SIR = 0.6, 95% CI = 0.4-1.0). The risk was increased in cancers of the gallbladder (SIR = 2.8, 95% CI = 1.1-5.8) and thyroid gland (SIR = 2.1, 95% CI = 1.0-4.8). The risks of lung and gallbladder cancer were lowest and highest, respectively, in those subjects with profound and severe ID, a group who also had significantly elevated SIRs for brain cancer (SIR = 3.46, 95% CI = 1.5-14.4) and testicular cancer (SIR = 9.9, 95% CI = 1.2-35.6). The incidence of cancer among people with ID was comparable with the general population, despite their low prevalence of smoking and apparently decreased diagnostic screening activity. Nevertheless, a few types of cancer carry a higher risk in the population with ID, possibly because of conditions typical among this group, such as gallstones or oesophageal reflux.