Multiple nontraumatic peritoneal and mesenteric emergencies are encountered at imaging of patients in the emergency department. Peritoneal and mesenteric emergencies are usually detected in patients in the emergency department during evaluation of nonspecific abdominal pain. A high index of suspicion is required for the establishment of early diagnosis and aversion of life-threatening complications in cases of peritoneal carcinomatosis, nontraumatic hemoperitoneum, and peritonitis. A correct diagnosis of omental infarction, mesenteric adenitis, and mesenteric panniculitis helps patients primarily by avoiding unnecessary surgery. In this review article, we illustrate the cross-sectional imaging appearance of various nontraumatic peritoneal and mesenteric emergencies by emphasizing the role of the emergency radiologist in detecting and managing these entities.