Little attention may be paid during follow up of colorectal cancer patients to other medical problems because the follow up is normally focused upon the diagnosis of recurrence and the detection of metachronous neoplasms. Attention directed at improving the medical condition of patients would be justified if it were shown that other diseases had a significant effect upon survival. Review of a selected consecutive series of 207 patients included collection of data about variables relating to demography, pathology, presentation, smoking, present and past health, performance, surgery, complications, length of stay, mortality, follow up and cause of death. Significance of relationships between medical and surgical problems and the outcome was determined by analyses of variation. Medical problems were present in 79% of patients; correlated with advancing age. Medical problems were not associated with complications, or with inpatient death. Previous cerebrovascular accident, dementia, limited mobility and increasing numbers of problems were associated with prolonged stay. Prolongation of stay, however, was related mainly to surgical complications. Smoking, which was present in 50% of patients, did not alter performance status, stage or substage, stay or survival significantly. Smoking and respiratory complications were associated significantly. Patients with heart or peripheral vascular disease had significantly poorer survival (P = 0.007) than those without those problems. Survival was reduced significantly for patients known to have diabetes, cardiovascular and cerebrovascular disease and limited mobility. Other malignant neoplasms were responsible for 18% of deaths which were unrelated to colorectal cancer. Residual or recurrent colorectal cancer had a more rapid adverse influence upon outcome than did medical problems.(ABSTRACT TRUNCATED AT 250 WORDS)