To determine why the prognosis for colorectal cancer in young adults is poor, survival and prognostic factors in patients under 40 years of age were compared with those in patients between 40 and 50 years of age. In a 10-year period, 122 patients less than 50 years of age (88 between 40 and 50 years) presented at the Victoria General Hospital in Halifax, NS, with colorectal cancer. Their charts were retrospectively reviewed. Follow-up was obtained for all patients. Of the 34 patients younger than 40 years, 71% (24) were men compared with 38% (33) of older patients. Symptoms, their duration and the location of primary tumours were similar in the two groups. Patients younger than 40 years presented with advanced lesions (Dukes' stages C and D) in 67% of cases compared with 52% of the older group. Mucinous tumours were twice as common in patients less than 40 years old (p = 0.036) and actuarial survival rates were lower at all stages for the same group. The authors conclude that the poorer prognosis in patients less than 40 years of age is not due to late symptom reporting or delay in diagnosis, but to more aggressive disease.