Acute abdominal pain and abdominal mass are intimately connected; therefore, the diagnostic process for evaluating abdominal pain and abdominal masses is largely the same and has been preserved since ancient times. The primary goals in the management of patients with abdominal pain and/or abdominal mass are to establish a differential diagnosis by obtaining a clinical history, to refine the differential diagnosis with a physical examination and appropriate studies, and to determine the role of operative intervention in the treatment or refinement of the working diagnosis. This review describes the process of diagnosing abdominal pain, including taking a clinical history and performing a physical examination. Investigative studies, including laboratory tests, imaging, and pathology are reviewed. Management, including surgical treatment, is discussed. Tables describe intraperitoneal and extraperitoneal causes of acute abdominal pain, frequency of specific diagnoses in patients with acute abdominal pain, and common abdominal signs and findings noted on physical examination. Figures show abdominal pain in specific locations, a data sheet, the differential diagnosis of an abdominal mass by quadrant or region, characteristic patterns of abdominal pain, acute appendicitis with associated appendicolith, bilateral adrenal masses, adrenocortical carcinoma, retroperitoneal leiomyosarcoma, pancreatic mass, a sagittal ultrasonogram of the pancreas, ultrasonograms of the liver, a dark and well circumscribed abdominal mass, gastroesophageal junction adenocarcinoma, and percutaneous biopsy of a large abdominal mass. An algorithm outlines the assessment of acute abdominal pain and abdominal mass. This review contains 16 figures, 5 tables, and 164 references. Keywords:  anatomy, swellings, inflammatory, opioid, palpatation, PET, COVID 19

Acute abdominal pain and abdominal mass are intimately connected; therefore, the diagnostic process for evaluating abdominal pain and abdominal masses is largely the same and has been preserved since ancient times. The primary goals in the management of patients with abdominal pain and/or abdominal mass are to establish a differential diagnosis by obtaining a clinical history, to refine the differential diagnosis with a physical examination and appropriate studies, and to determine the role of operative intervention in the treatment or refinement of the working diagnosis. This review describes the process of diagnosing abdominal pain, including taking a clinical history and performing a physical examination. Investigative studies, including laboratory tests, imaging, and pathology are reviewed. Management, including surgical treatment, is discussed. Tables describe intraperitoneal and extraperitoneal causes of acute abdominal pain, frequency of specific diagnoses in patients with acute abdominal pain, and common abdominal signs and findings noted on physical examination. Figures show abdominal pain in specific locations, a data sheet, the differential diagnosis of an abdominal mass by quadrant or region, characteristic patterns of abdominal pain, acute appendicitis with associated appendicolith, bilateral adrenal masses, adrenocortical carcinoma, retroperitoneal leiomyosarcoma, pancreatic mass, a sagittal ultrasonogram of the pancreas, ultrasonograms of the liver, a dark and well circumscribed abdominal mass, gastroesophageal junction adenocarcinoma, and percutaneous biopsy of a large abdominal mass. An algorithm outlines the assessment of acute abdominal pain and abdominal mass. This review contains 14 figures, 5 tables, and 143 references.