Background:Endoscopic ultrasound (EUS)-guided fine needle aspiration biopsy (EUS-FNA) has extended the application of EUS. Through this procedure, cytopathological examination of abnormalities discovered on imaging studies can be made. EUS-FNA has become an important diagnostic tool as it permits sampling of lesions not amenable to percutaneous biopsy or which are too small to be identified by other imaging modalities.EUS uses have been expanded to include the upper and lower gastrointestinal tracts, hepatobiliary and portal systems, and the anal sphincter, as well as the diagnosis and staging of esophageal, gastric, pancreaticobiliary and mediastinal lesions.Objective: Assessment of the value of the EUS-FNA in the diagnosis of gastrointestinal, pancreatic & mediastinal lesions.Methods:This prospective study will include a suitable number of patients referred for an endoscopic ultrasound-guided fine needle aspiration biopsy (EUS-FNA) from the gastrointestinal wall, the pancreas and the mediastinum.All patients will be subjected to;•Complete medical history.•Complete physical examination.•Routine laboratory tests which usually include complete blood count (CBC), coagulation profile, liver and renal function tests, and tumor markers if needed.•Abdominal ultrasound.•Computed tomography (CT), or magnetic resonance imaging (MRI) of the chest, abdomen, and pelvis if possible.All patients will be subjected to endoscopic ultrasound exam using a Pentax EG 3830-UT linear-array echoendoscope connected to a Hitachi EUS-7500 machine.All patients will be under deep sedation with propofol and subjected to endoscopic ultrasound-guided fine needle aspiration biopsy (EUS-FNA) using a needle 19 or 22 gauge in diameter.Fine needle aspiration biopsy will be taken from different sites including;•Gastrointestinal wall sites, comprised of the esophageal, gastric, duodenal and rectal wall lesions.•Pancreatic solid and cystic lesions.•Extraluminal, abdominal and mediastinal lymph nodes.•Mediastinal lesions.The fine needle aspiration biopsy (FNA) material will be spread over glass slides and fixed by alcohol (95% ethanol), and the rest of the material will be preserved in formalin. The material will then be examined by an expert cytopathologist. Results: In our study we found the size of the lesion not to be a determining factor in the accuracy of the endoscopic ultrasound-guided fine needle aspiration diagnosis. We found that the nature of the lesion and the system affected were factors that affect the accuracy of diagnosis of this modality.