Patients whose colons were resected for carcinoma were studied in order to determine the relationship between clinical findings-which included development of postoperative delirium- and intramitochondrial inclusion bodies (MI) in the neurons in the colon. Twenty-three patients had MI and 24 patients did not. Preoperative dementia was present in 9 (39.1%) of the 23 patients with MI, and in 7 (29.2%) of the 24 without it. Postoperative delirium developed in 13 (56.3%) of the 23 with MI, and in 5 (20.8%) of the 24 without it (p < 0.05). Excluding preoperative dementia, postoperative delirium developed in 5 (35.7%) of the 14 with MI, and in none of the 17 without it. Changes in the neurons in the colon were not related to dementia. The changes may have been related to the functions of the central nervous system, because patients with MI were likely to develop postoperative delirium.