The incidence and significance of histologic vascular and/or neural invasion in 77 patients with colorectal carcinoma treated over a 6-year period were analyzed retrospectively. Vascular invasion was found in 37.6% of patients and neural invasion in 14.3%. The following three types of vascular invasion were identified: tumor lining epithelium, tumor thrombi, and destruction of the vessel wall. The incidence of metastases in patients with vascular invasion was 60% as opposed to 17% in those without vascular invasions (P less than 0.0001). Survival in these patients was 29.7% and 62.2%, respectively (P less than 0.003). Metastases were found in 72.7% of patients with neural invasion, as opposed to 27% of those without neural invasion (P less than 0.01). Survival was 29.6% as opposed to 57.7% in those without neural invasion (P less than 0.003). Even among patients in the same Dukes' stage, prognosis, as determined by incidence of recurrence, metastases, and survival, was worse significantly among those patients demonstrating vascular invasion (P less than 0.03). Examination of patients with colorectal carcinoma for the presence of vascular and neural invasion may provide useful information for determining future treatment and prognosis.