Objectives: Although idiopathic pancreatitis is common, the natural history is not well studied, and the best diagnostic approach to both single and multiple attacks remains undefined. Methods: We prospectively evaluated patients with idiopathic pancreatitis over a 10-year period, and clinical information for each episode was reviewed. Endoscopic ultrasound (EUS) was performed in all patients. Patients with microlithiasis or bile duct stones were referred for cholecystectomy and endoscopic retrograde cholangiopancreatography (ERCP), respectively. For those with a single attack, if EUS was normal or chronic pancreatitis or pancreas divisum was diagnosed, the patient was followed up for recurrence. For those with multiple attacks and a negative EUS, ERCP and sphincter of Oddi manometry with endoscopic therapy as appropriate were recommended. All patients were followed up in the long term to evaluate for recurrent pancreatitis, the primary study end point. Results: Over the study period, 201 patients were identified (80 single attack, 121 multiple attacks; mean age 53 years, range 17-95 years, s.d. 16.3 years; and 53% female). After EUS, 54% of patients with a single attack were categorized as idiopathic, and for multiple attacks sphincter of Oddi dysfunction (SOD) was the most common diagnosis (41%). Long-term follow-up (median 37 months; interquartile range 19-70 months) documented recurrence of pancreatitis in 15 (24%; 95% confidence interval (CI), 15-38%) patients with a single attack and in 48 (49%; 95% CI, 38-62%) patients with multiple attacks. Despite endoscopic therapy, patients with pancreas divisum and SOD had relapse rates of 50% (95% CI, 35 to 68%) and 55% (95% CI, 31 to 82%), respectively. Conclusions: Following a single idiopathic attack of pancreatitis and a negative EUS examination, relapse was infrequent. Despite endoscopic therapy, patients with multiple attacks, especially those attributed to pancreas divisum and SOD, had high rates of recurrence. EUS may be a useful, minimally invasive tool for the diagnostic evaluation of idiopathic pancreatitis.