Laparoscopic Nissen fundoplication has been applied with increasing frequency in the treatment of gastroesophageal reflux disease. The aim of this study was to determine the variables that predict outcome of laparoscopic Nissen fundoplication. A multivariate analysis was performed on data from 199 consecutive patients undergoing laparoscopic Nissen fundoplication. Variables included age, sex, body mass index, primary symptoms, clinical response to acid suppression therapy, erosive esophagitis, 24-hour esophageal pH score, and the percentage of time the esophageal pH was less than 4 on 24-hour pH monitoring, lower esophageal sphincter competence, status of the esophageal body motility, hiatal hernia, carditis, intestinal metaplasia of cardiac epithelium limited to the gastroesophageal junction, and Barrett's esophagus of any length. Clinical outcome was obtained from all patients at a median follow-up of 15 months (range 6 to 74 months) after surgery. One hundred seventy-three patients had an excellent or good outcome (87%) and 26 had a fair or poor outcome. Three factors were significantly predictive of a successful outcome: an abnormal 24-hour pH score (odds ratio = 5.4; 95% confidence interval [CI] = 1. 9-15.3), a typical primary symptom (odds ratio = 5.1; 95% CI = 1. 9-13.6), and a clinical response to acid suppression therapy (odds ratio = 3.3; 95% CI = 1.3-8.7). We conclude that 24-hour pH monitoring provides the strongest outcome predictor of laparoscopic Nissen fundoplication and that outcome is based more on the correct identification of the disease than on its severity.