Nutritional screening and assessment are considered essential steps in nutritional care for cancer patients, malnutrition remains underreported in clinical practice. The aim of this study was to analyse the clinical usefulness of the Patient-Generated Subjective Global Assessment short form (PG-SGA SF^©) for nutritional screening in patients with head and neck cancer (HNC). This is a multicentre, cross-sectional study involving patients with HNC. The final score of the PG-SGA SF^© was obtained and the nutritional status was diagnosed using the Patient-Generated Subjective Global Assessment (PG-SGA)^®, classifying them as well-nourished or malnourished. Receiver operating characteristic curve, ordinal logistic regression, and C-statistic were used. In total, 353 patients with HNC were enrolled and the prevalence of malnutrition, according to the PG-SGA^®, was 64.02% and the median final score of PG-SGA SF^© was 11 points. The final score of the PG-SGA SF^© had high accuracy (area under the curve = 0.915), and scores ≥9 had the best performance in diagnosing malnutrition. PG-SGA SF^© final score ≥9 was associated with malnutrition (odds ratio = 28.32, 95% confidence interval= 15.98–50.17), with excellent discriminatory power (C-statistic = 0.872). In conclusion, the PG-SGA SF^© demonstrated excellent performance for nutritional screening in patients with HNC. Given that it is a simple instrument that is faster to administer than the PG-SGA^®, we recommend its use in clinical practice among such patients.