Background: Endoscopic ultrasound (EUS) is an accurate technique for the study of pancreatic and billiary diseases. The clinical usefulness of EUS in patients (PT) with idiopathic acute relapsing pancreatitis (IARP) is uncertain. Aim: To prospectively assess the clinical usefulness and diagnostic accuracy of EUS in patients with IARP. Material and Methods: IRB approval obtained for the study. Design: Prospective. Period of inclusion: 08/02-07/04. Inclusion Criteria: 1.) PT with 2 or more episodes of pancreatitis (abdominal pain + elevation of pancreatic enzymes) of unknown etiology after clinical history (drugs, etc), laboratory analysis, ultrasound and CT scan have been performed; 2.) PT > 18 years. Exclusion Criteria: 1.) PT refuses to participate. EUS exam (conscious sedation): GF-UM160 Olympus. Statistical analysis: Descriptive analysis of results obtained: Discrete variables (%), continuous variables (mean + SD; median). Results: During the aforementioned period of time 140 consecutive PT meeting criteria for the study have been included. PT characteristics: M/F (44%/56%), age (60.3 + 14.5 years [64]), smoker (yes: 37%; 8.8 + 11.1 c/d [0]), alcohol (yes 47%; 20.5 + 21.3 g/d [10]), BMI (28.6 + 5.0 kg/m2 [28.3]), cardiac disease (21%), diabetes mellitus (14%), COPD (6%), prior endoscopy (56%). EUS examination showed abnormal findings that may be responsible for patient IARP (not identified in prior studies) in 78% of PT evaluated/included (109 of 140 PT): Sludge/microlithiasis (64 PT), common bile duct (CBD) stones (17 PT), chronic pancreatitis by EUS criteria (17 PT), pancreas divissum (6 PT), pancreatic tumor (5 PT). To date, gold standard confirmation of these EUS diagnosis has been obtained in 101 of those 109 PT (93%). EUS findings could not be confirmed in 8 PT with EUS diagnosis of mild chronic pancreatitis. EUS diagnosis (etiology) was correct in 97 of 101 PT in whom gold standard confirmation could be obtained (96%) (ERCP exam proved EUS to be wrong in 2 PT with EUS diagnosis of pancreas divissum and 2 PT with presumed CBD stones). Overall, EUS identified a potential etiology for IARP that was ultimately confirmed in 97 of 140 PT included in the study (69%). Conclusions: 1.) EUS may be useful to identify the underlying etiology in 2 out of 3 PT presenting with IARP. 2.) The clinical usefulness, elevated diagnostic accuracy and potential economic impact of EUS for the evaluation of PT with IARP favors its use in clinical practice. Background: Endoscopic ultrasound (EUS) is an accurate technique for the study of pancreatic and billiary diseases. The clinical usefulness of EUS in patients (PT) with idiopathic acute relapsing pancreatitis (IARP) is uncertain. Aim: To prospectively assess the clinical usefulness and diagnostic accuracy of EUS in patients with IARP. Material and Methods: IRB approval obtained for the study. Design: Prospective. Period of inclusion: 08/02-07/04. Inclusion Criteria: 1.) PT with 2 or more episodes of pancreatitis (abdominal pain + elevation of pancreatic enzymes) of unknown etiology after clinical history (drugs, etc), laboratory analysis, ultrasound and CT scan have been performed; 2.) PT > 18 years. Exclusion Criteria: 1.) PT refuses to participate. EUS exam (conscious sedation): GF-UM160 Olympus. Statistical analysis: Descriptive analysis of results obtained: Discrete variables (%), continuous variables (mean + SD; median). Results: During the aforementioned period of time 140 consecutive PT meeting criteria for the study have been included. PT characteristics: M/F (44%/56%), age (60.3 + 14.5 years [64]), smoker (yes: 37%; 8.8 + 11.1 c/d [0]), alcohol (yes 47%; 20.5 + 21.3 g/d [10]), BMI (28.6 + 5.0 kg/m2 [28.3]), cardiac disease (21%), diabetes mellitus (14%), COPD (6%), prior endoscopy (56%). EUS examination showed abnormal findings that may be responsible for patient IARP (not identified in prior studies) in 78% of PT evaluated/included (109 of 140 PT): Sludge/microlithiasis (64 PT), common bile duct (CBD) stones (17 PT), chronic pancreatitis by EUS criteria (17 PT), pancreas divissum (6 PT), pancreatic tumor (5 PT). To date, gold standard confirmation of these EUS diagnosis has been obtained in 101 of those 109 PT (93%). EUS findings could not be confirmed in 8 PT with EUS diagnosis of mild chronic pancreatitis. EUS diagnosis (etiology) was correct in 97 of 101 PT in whom gold standard confirmation could be obtained (96%) (ERCP exam proved EUS to be wrong in 2 PT with EUS diagnosis of pancreas divissum and 2 PT with presumed CBD stones). Overall, EUS identified a potential etiology for IARP that was ultimately confirmed in 97 of 140 PT included in the study (69%). Conclusions: 1.) EUS may be useful to identify the underlying etiology in 2 out of 3 PT presenting with IARP. 2.) The clinical usefulness, elevated diagnostic accuracy and potential economic impact of EUS for the evaluation of PT with IARP favors its use in clinical practice.