Colorectal cancers in 92 patients aged 45 years and under presenting over a 20-year period (1970-1990) were studied. A delay of more than 4 months in presentation was seen in 27 per cent of patients. All underwent surgery, 14 per cent emergency and 86 per cent elective, and follow-up was available for 91 patients. Overall, 14 per cent of patients had Dukes A tumours, 32 per cent Dukes B, 36 per cent Dukes C and 18 per cent Dukes 'D'. Local recurrence occurred in eight (9 per cent) of the 92 patients and overall 5- and 10-year survival rates were 61 and 59 per cent. Multivariate analysis identified independent risk factors for local recurrence to be mucinous carcinoma (relative effect 4.9) and the presence of intramural vascular invasion by tumour (relative effect 9.4). For overall survival, independent risk factors were involvement of the regional lymph nodes by tumour (relative effect 2.0), extramural invasion by tumour cells (relative effect 3.0), tumour size (relative effect 1.8) and the presence of metastatic disease at initial diagnosis (relative effect 3.7).