Acute abdominal pain is one of the most frequent causes of admission to emergency departments. However, there is a shortage of detail information showing the difference of outcomes or etiology of acute abdominal pain according to age. We therefore conducted an epidemiological analysis to reveal the difference between age on outcomes and etiology of acute abdominal pain using an administrative database associated with the Diagnosis Procedure Combination (DPC) system. We obtained discharge data relating to 12,209 patients with acute abdominal pain from 931 DPC participation hospitals between 2009 and 2011 in Japan. We compared length of hospital stay (LOS), in-hospital mortality, and etiology of acute abdominal pain between age categories. Patients were divided into five age groups as follows: < 20 (n = 1,106), 20-39 (n = 3,353), 40-59 (n = 2,925), 60-79 (n = 3,144), and ≥ 80 years (n = 1,681). Longer LOS and higher in-hospital mortality were observed in patients aged ≥ 80 years (p < 0.001). Regarding etiologies of acute abdominal pain, intestinal infection or acute appendicitis were more frequent in patients aged < 20 or 20-39 years, while ileus or cholelithiasis were more frequent in patients aged 60-79 or ≥ 80 years in both male and female patients (p < 0.001). This study demonstrated the significant differences between age with regard to the patient outcomes and etiology of acute abdominal pain. The current findings highlight the importance of improving the quality of medical care for patients with acute abdominal pain.