Adenocarcinoma of the colon and rectum in patients less than 40 years of age. From 1962 to 1988, 50 of 801 patients with adenocarcinoma of the colon and rectum treated at the National Naval Medical Center were less than 40 years old. Symptoms were present in 47 of the younger patients at presentation. The mean duration of time from the onset of symptoms to diagnosis in this group was 4.9 months. Risk factors for carcinoma of the colon and rectum were identified in 14 of 50 patients less than 40 years old. A significantly greater proportion of patients less than 40 years old had Stage C disease compared with the older group of patients (42 versus 22 per cent, p = 0.014). Stage B disease was more common in patients more than 40 years of age (44.8 versus 26.0 per cent, p = 0.014). The proportion of patients with Stages A and D disease was similar in both age groups. The cumulative survival rate in this group at five and ten years was 43 and 34 per cent, respectively. The five year survival rate in patients less than 40 years old with Stage B disease was 76 per cent and with Stage C disease, 37 per cent. All young patients with Stage D disease were dead at 28 months. Synchronous and metachronous carcinomas of the colon and rectum were uncommon in patients less than 40 years old. Patients less than 40 years of age with carcinoma of the colon and rectum are usually symptomatic and have advanced disease at the time of presentation. Survival time for these patients for each stage of disease is similar to the over-all population of patients with carcinoma of the colon and rectum. 