To analyze the mechanisms by which Nissen fundoplication controls gastroesophageal reflux, the pre- and post-operative manometric findings in 34 patients were compared. The postoperative assessment showed an increase in both the infradiaphragmatic length and basal pressure of the lower esophageal sphincter and a notable improvement in esophageal motility (increase in the amplitude of the waves and decrease in the mean percentage of deglutitions without response and tertiary waves) in those who preoperatively presented with defective esophageal peristalsis.