Three hundred and twenty-two patients who underwent curative resection of rectal adenocarcinoma from 1970 to 1985 were studied retrospectively to evaluate the prognostic value of five histological findings at the invasive front of the lesions: 1) many small clusters of undifferentiated cancer cells ahead of the invasive front of the lesion; 2) a poorly demarcated invasive front; 3) poorly differentiated cancer cells in the invasive front; 4) intramural tumor spread; and 5) severe grade of perineural invasion. The analysis showed a significantly higher recurrence rate in the presence of each finding (p < 0.05-0.005). There was also a significant correlation between the actuarial survival rate and each finding (p < 0.01-0.001). The survival curve of Dukes' B or C tumors with at least one of those 5 findings has a significantly worse outcome than those without any (p < 0.01, respectively). Moreover, the survival curve of Dukes' B patients with one or more findings was rather worse than that of Dukes' C patients without any. In conclusion, the presence of these 5 factors at the invasive front of rectal cancer appears to indicate a vigorous biological attitude of tumor. These factors provides valuable prognostic information, independent of Dukes' stage.