The relative survival of all patients (n = 61,769) in the entire Swedish population reported to have a malignant tumour of the colon and rectum between 1960 and 1981 was analysed with special reference to patients under 40 years of age. The 5-year relative survival rate of patients with a tumour of the colon, irrespective of histopathological diagnosis, was 62.0 per cent below the age of 40 years and 44.4 per cent in those 40 years of age or older (P less than 0.05). The corresponding figures for patients with a tumour of the rectum were 46.6 per cent and 39.1 per cent, respectively. When the relative survival was analysed separately for patients with a histopathologically demonstrated adenocarcinoma, the 5-year survival rate among patients with a cancer of the colon was 50.9 per cent in patients below 40 years of age and 48.6 per cent in those 40 years of age or older. In patients with adenocarcinoma of the rectum, the 5-year relative survival rate was 41.1 per cent in patients younger than 40 years of age and 40.7 per cent in patients 40 years of age or older. Thus, patients below the age of 40 years with an adenocarcinoma of the colon and rectum as a group appear to have the same or even a better prognosis than older patients if all tumours are considered, irrespective of histopathological diagnosis.