We evaluated the prevalence, diagnosis, and treatment of dumping syndrome (DS) following Nissen fundoplication in 50 consecutive infants and children who underwent the operation for gastroesophageal reflux. Examination included a preoperative dietary assessment with emphasis on specific postprandial clinical symptoms and technetium scintigraphy to evaluate gastric emptying. In the immediate postoperative period, postprandial glucose levels were examined in all patients with symptoms clinically suggestive of DS. In the late postoperative period (6 months to 5.5 years), all patients with more than one specific clinical symptom of DS were further evaluated by glucose tolerance test (GTT), HbA1C levels, and gastric technetium scintigraphy. DS was diagnosed in 15 patients (30%). Five patients had immediate severe DS (SDS), and 10 in the late postoperative course had latent postoperative DS (LDS). In all patients with DS, preoperative and postoperative gastric emptying scan T1/2 did not show any statistical significance. High levels of HbA1C ranging from 7.9 to 9% (mean, 8.25 +/- 0.5) were found in only three patients. Treatment included parenteral nutrition in one patient. All the others were successfully managed with nutritional manipulation alone, using a combination of lactose-free formula and fat emulsion. In patients whose postprandial symptoms persisted, pectin 5-15 g/day divided into six doses was added to the diet. Following 6 months of dietary treatment, the postprandial normoglycomic response was restored. Eleven patients experienced complete resolution of symptoms (78.5%), and three patients (21.4%) showed significant clinical improvement. This study indicates that DS is a common complication following Nissen fundoplication. The GTT is the most reliable examination for establishing the diagnosis. Treatment is simple and effective. The technetium gastric emptying scan and HbA1C level do not play a significant role in the diagnosis.