In patients scheduled for surgery, nutritional disorders worsen during the perioperative period, which is often a risk factor for postoperative complications. The aim of the study was to determine relationship between the preoperative nutritional status of elderly people with stomach, pancreatic and colon cancer and the incidence of postoperative complications and the length of hospital stay. The study included 143 patients with gastrointestinal cancer, aged 65–68, qualified for surgery. Mini Nutritional Assessment, body mass index questionnaires and medical records were used. Malnutrition was found in 9.8%, and a risk of malnutrition in 53.5% of the respondents. Body mass index showed overweight in 28% and obesity in 14% of the patients. Complications occurred in all types of nutritional status, the most common were those requiring intensive care unit treatment (36.8%), pancreatic and biliary fistulas (29.4%) and surgical site infections (58.2%). Gastric cancer patients at risk of malnutrition stayed longer in the hospital. Postoperative complications and longer hospital stays were observed more frequently in cases of overweight, obesity, malnutrition and its risk. Disturbances in the nutritional status, in the form of malnutrition and its risk, as well as overweight and obesity, determined more frequent occurrence of postoperative complications and longer hospital stay.