Acute abdomen represents about 50% of admission in developed countries. It comprises different etiologies, each with a distinct clinical presentation and evolution. Irrespective of the cause, it is related to high morbidity and a non-negligible mortality rate. Prompt diagnosis and treatment are essential to decrease morbidity and mortality and the cost-efficiency of health systems. Point-of-care ultrasound (POCUS), a bedside ultrasound performed by a non-radiologist, has shown great potential in many clinical conditions, including the acute abdomen. It allows, first of all, to quickly assess the abdomen in what we call a rule-out modality, and in more experienced hands can be used for a more focused examination which we call rule-in modality. The findings of free fluid POCUS in patients with acute abdomen should guide the assessment of the severity, the diagnostic workflow, and the timing for surgical consultation.