Objective:To investigate the etiology of acute pancreatitis (AP) in Inner Mongolia and its correlation with gender, age and severity of the disease.Methods:From January 2015 to December 2018, the clinical data of 4 168 patients with AP admitted to six large tertiary general hospitals in Inner Mongolia were retrospectively collected and the etiology of AP was summarized. The etiology of different gender, age and severity of AP was analyzed. Chi-square test and adjusted chi-square test were used for statistical analysis.Results:The etiology of 4 168 patients with AP included 2 060 cases (49.4%) of biliary diseases, 608 cases (14.6%) of hypertriglyceridemia, 579 cases (13.9%) of idiopathic causes, 399 cases (9.6%) of alcohol intake, 256 cases (6.1%) of overeating and 266 cases (6.4%) of other causes. The proporation of biliary AP in male patients was lower than that in female patients (39.2%, 917/2 340 vs. 62.5%, 1 143/1 828), however the proporations of hypertriglyceridemic AP, alcoholic AP, overeating AP and AP caused by other causes were all higher than those of female patients (17.4%, 406/2 340 vs. 11.1%, 202/1 828; 14.9%, 349/2 340 vs. 2.7%, 50/1 828; 7.6%, 178/2 340 vs. 4.3%, 78/1 828 and 7.1%, 165/2 340 vs. 5.5%, 101/1 828), and the differences were statistically significant ( χ2=223.645, 32.693, 175.859, 19.858, and 4.001, all P<0.05). The proporation of biliary AP in patients aged between 19 and 59 years was lower than that in patients aged less than 18 years and over 60 years (42.4%, 1 100/2 593 vs. 55.1%, 54/98 and 61.3%, 906/1 477), and the differences were statistically significant ( χ2=6.199 and 134.746, both P<0.016). The proporation of hypertriglyceridemic AP in patients aged over 60 years was lower than that in patients aged between 19 and 59 years and less than 18 years (6.9%, 102/1 477 vs. 18.9%, 491/2 593 and 15.3%, 15/98), and the differences were statistically significant ( χ2=109.403 and 9.430, both P<0.016). The proporation of idiopathic AP in patients aged between 19 and 59 years was higher than that of patients aged over 18 years (14.8%, 384/2 593 vs. 6.1%, 6/98), and the difference was statistically significant ( χ2=5.750, P<0.016). The proporation of alcoholic AP in patients aged between 19 and 59 years was higher than that of patients aged less than 18 years and over 60 years (11.7%, 303/2 593 vs. 1.0%, 1/98 and 6.4%, 95/1 477), the differences were statistically significant ( χ2=10.718 and 29.435, both P<0.016). And the proporation of other causes of AP of the patients aged less than 18 years was higher than those of patients aged between 19 and 59 years and over 60 years (14.3%, 14/98 vs. 5.9%, 152/2 593 and 6.8%, 100/1 477), and the differences were statistically significant ( χ2=0.559 and 0.959, P<0.016). Among the biliary causes, the proporation of moderate severe acute pancreatitis (MSAP) was higher than those of mild acute pancreatitis (MAP) and severe acute pancreatitis (SAP) (59.6%, 336/564 vs. 47.5%, 1 522/3 204 and 50.5%, 202/400), and the differences were statistically significant ( χ2=27.959 and 7.814, both P<0.016). In terms of hypertriglyceridemia and other causes, the proporation of MAP was the lowest (12.7%, 407/3 204 and 4.0%, 127/3 204), and the proporations were statistically significant compared with the proporation of MSAP and SAP (23.0%, 130/564; 12.2%, 69/564 and 17.8%, 71/400; 17.5%, 70/400; χ2=42.013, 7.874, 66.520 and 126.094, all P<0.016). The proporation of MSAP was the lowest among the idiopathic causes (0.7%, 4/564), and the difference was statistically significant compared with the proporation of MAP and SAP (16.6%, 533/3 204 and 10.5%, 42/400; χ2=99.540 and 49.369, both P<0.016). The proporation of SAP was lower than that of MAP, and the difference was statistically significant ( χ2=9.983, P<0.016). In alcoholic and overeating causes, the proporation of MAP was the highest (11.4%, 365/3 204, 7.8%, 250/3 204), and the differences were statistically significant compared with MSAP and SAP (3.5%, 20/564; 0.9%, 5/564; 3.5%, 14/400 and 0.2%, 1/400; χ2=32.182, 23.537, 36.358 and 31.307, all P<0.016). Conclusions:Consistent with reports in most areas of China, the etiology of AP in Inner Mongolia area is mainly biliary diseases and hypertriglyceridemia. Most of the patients with biliary acute pancreatitis are female, mostly in patients more than 60 years old and most of them are MSAP. Hyperlipidemic and alcoholic AP are more common in middle-aged and young male patients, and are mostly MSAP and SAP; while most of alcoholic AP is MAP.