&NA;To confirm the prognostic significance of the DNA index (DI) in cases of rectal cancer, the nuclear DNA content of tumor cells was examined in 184 cases of rectal cancer treated with curative surgery, and the incidence of lymph node metastasis and recurrence of the cancer was analyzed. The incidence of lymph node metastasis was 43.9 percent in cases with aneuploidy (DI above 1.5), being statistically different from the 18.0 percent incidence in cases with diploidy(P<0.001). Although the extent of lymph node metastasis was limited to adjacent lymph nodes in cases with diploidy, distant lymph node metastases were frequent in cases with aneuploidy, especially in those with a DI above 1.5. Furthermore, the incidence of recurrence of cancer, and especially of local recurrence, was significantly higher(P<0.001) in cases with aneuploidy (DI above 1.5) than in cases with diploidy and aneuploidy (DI below 1.4). These findings indicate the significant value of the DNA index for the prediction of lymph node metastasis and local recurrence in patients with rectal cancer.