Objective: To study the use of serial ultrasound gastric residual volume (GRV) measurements in predicting feed intolerance in critically ill patients. Patients and methods: This study was conducted in various intensive care units (ICUs) of All India Institute of Medical Sciences, New Delhi. Forty-three critically ill patients aged more than 18 years were studied for a total of 130 enteral feeding days. Gastric residual volume was obtained by calculating the antral cross-sectional area (CSA), which is the product of anteroposterior (AP) and craniocaudal (CC) diameters of gastric antrum obtained using ultrasound in the right lateral decubitus position. A baseline measurement was done before the initiation of the enteral feed and termed GRV0, the ultrasound scanning was repeated every 1 hour for the first 4 hours and termed GRV1, GRV2, GRV3, and GRV4, respectively, and the patients were watched for feed intolerance. The receiver operating characteristic (ROC) curves were constructed to correlate the GRV at each time with feed intolerance. Results: The data from 43 medical and surgical critically ill patients were analyzed. Out of 130 feeding days, 13 were noted to be feed intolerant. Gastric residual volume at the end of the fourth hour of feed, that is, GRV4 was the best predictor of feed intolerance with 99.3% area under the curve (AUROC), sensitivity of 99%, specificity of 99.3%, and 95% CI, 0.89–0.98 followed by GRV3, with AUROC of 96% and sensitivity and specificity of 92.3 and 96%, respectively, with 95% CI, 0.92–0.99.