Carl Wernicke described the disease bearing his name in 1881 and reported three cases characterized by the presence of mental confusion, ataxia, and ophthalmoplegia. Wernicke's disease is mainly observed in alcoholic patients, due to decreased vitamin intake as a consequence of an unbalanced diet, and a reduction of absorption due to the effects of alcohol. Likewise, inadequate vitamin intake is prevalent in older patients. Wernicke's encephalopathy due to inappropriate total parenteral nutrition (TPN) occurs infrequently; recently, there is an increase in the literature concerning Wernicke's encephalopathy in patients after general and bariatric surgeries. We present two cases of Wernicke's encephalopathy after oncologic gastrointestinal surgery by failure to administer vitamin B1 during TPN; to our knowledge, these are the first two cases of Wernicke's encephalopathy after colorectal surgery for cancer. In our opinion, timely diagnosis and treatment are mandatory to avoid nonfunctional recovery and consequent malpractice legal actions as well as an increase in the health-care costs correlated with the prolonged hospital stay and with the nonfunctional recovery.