The scored Patient-Generated Subjective Global Assessment (PG-SGA) is considered to be the most appropriate tool for detecting malnutrition in cancer patients. In particular, malignant tumours derived from the gastrointestinal tract may impair nutrient intake and absorption and cause malnutrition. We carried out a cross-sectional study to assess the nutritional status and related factors of patients with gastrointestinal cancer. Nutritional status was determined using the scored PG-SGA in patients (n 498) with advanced gastrointestinal cancer admitted to the Gastrointestinal Medical Oncology Unit at Beijing Cancer Hospital between 1 August 2012 and 28 February 2013. The possible related factors including age, sex, hospitalisation frequency and pathology were explored. We found that 98 % of the patients required nutrition intervention and 54 % of the patients required improved nutrition-related symptom management and/or urgent nutritional support (PG-SGA score ≥ 9). Factors related to malnutrition were age (r 0·103, P< 0·01), hospitalisation frequency (r − 0·196, P< 0·01) and sex (the prevalence of malnutrition was higher in men than in women (9·88 v. 8·54, P< 0·01)). Patients with rectal cancer had a lower risk of malnutrition than patients with other types of gastrointestinal cancer (F= 35·895, P< 0·01). More attention should be paid to the nutritional status of gastrointestinal patients, especially those at a higher risk of malnutrition, such as elderly patients, those hospitalised for the first time, male patients and those with other types of gastrointestinal cancer except rectal cancer. The nutritional status of these patients should be evaluated and they should be given proper nutrition education and nutritional support in a timely manner.