Background: Complications from EUS guided FNA of cystic lesions of the pancre as are infrequent. Although several studies have evaluated infectious complicati ons of EUS-guided FNA in this setting, the frequency and the clinical significa nce of intracystic hemorrhage have not been determined. This study assessed the frequency of acute intracystic hemorrhage during EUS-guided FNA of pancreatic cystic lesions. The characteristic EUS appearance is described. Methods: EUS-guided FNA of pancreatic cyst lesions was per formed in 50 patients (July 2000 to June 2003). Patients were followed prospecti vely for the development of complications. Observations: Acute intracystic hemor rhage occurred during EUS-guided FNA at the site of aspiration in 3 patients (6 %: 95%confidence interval [1.3%, 16.6%]). Endosonographically, the bleeding manifested as a small hyperechoic area at the puncture site that progressed gradually over a few minutes to involve the majority of the cyst cavity. EUS-guided FNA was terminated when bleeding was observed. One patient was asymptomatic, but two patients experienced abdominal pain transiently. All patients were treated with a short course of orally administered antibiotics and were observed as out patients. Clinical history and laboratory parameters did not predict which patients were at risk for intracystic hemorrhage. Conclusions: Acute intracystic hemo rrhage is a rare complication of EUS-guided FNA; it has a characteristic EUS ap pearance. Recognition of this event is important, because it permits termination of the procedure and thereby minimizes the potential for more serious bleeding. Background: Complications from EUS guided FNA of cystic lesions of the pancre as are infrequent. Although several studies have some of the infectious infections involved in the setting of the EUS-guided FNA in this setting, the frequency and the clinical significa nce of intracystic hemorrhage have not been determined. The assessment of the frequency of acute intracystic hemorrhage during EUS-guided FNA of pancreatic cystic lesions. The characteristic EUS appearance is described. Methods: EUS-guided FNA of pancreatic cyst lesions was per formed in 50 patients (July 2000 to June 2003). Patients were followed prospecti vely for the development of complications. Observations: Acute intracystic hemorrhhage occurred during EUS-guided FNA at the site of aspiration in 3 patients (6%: 95% confidence interval [1.3%, 16.6%]) Endosonographically, the bleeding manifested as a small hyperechoic area at the puncture site that progressed gradually over a few minutes to involve the majority of the cyst cavity. EUS-guided FN A was terminated when bleeding was observed. One patient was asymptomatic, but two patients experienced abdominal pain transiently. All patients were treated with a short course of orally administered antibiotics and were observed as out patients. Clinical history and laboratory parameters did not predict which patients were at risk for intracystic hemorrhage. Conclusions: Acute intracystic hemo rrhage is a rare complication of EUS-guided FNA; it has a characteristic EUS ap pearance. Recognition of this event is important, because it permits termination of the procedure and thereby minimize the potential for more serious bleeding.