en Metabolic Surgery Metabolic Surgery Original Original Background: According to the IFSO worldwide survey report in 2014, 579517 bariatric operations have been performed in a year, of which nearly half the procedures were SG followed by RYGB. This procedure is a proven successful treatment of patients with morbid obesity which induces considerable weight loss and improvement of type 2 diabetes mellitus, insulin resistance, inflammation, and vascular function. In the present study, we aimed to build a machine based on a decision tree to mimics the surgeons pathway to select the type of bariatric surgery for patients.<br> Material and methods: We used patient&rsquo;s data from the National Bariatric Surgery registry between March 2009 and October 2020. A decision tree was constructed to predict the type of surgery. The validation of the decision tree confirmed using 4-folds cross-validation.<br> Results: We rich a decision tree with a depth of 5 that is able to classify 77% of patients into correct surgery groups. In addition, using this model we are able to predict 99% of bypass cases (Sensitivity) correctly. The waist circumference less than 126 cm and BMI equal to or more than 43 kg/m2, age equal to or greater than 30 years old, and being hypertensive or diabetes are the most important separators.<br> Discussion: The effects of all nodes have been studied before and the references confirmed the relations of them and surgery type.&nbsp; Bariatric surgery, Machine learning, Roux-en-Y Gastric Bypass, Sleeve Gastrostomy, Mini-gastric Bypass/One-Anastomosis Gastric Bypass  9 13 http://annbsurg.iums.ac.ir/browse.php?a_code=A-10-29-1&slc_lang=en&sid=1 Ali Sheidaei asheidaei@razi.tums.ac.ir 10031947532846001491 10031947532846001491 No Minimally Invasive Surgery Research Center, Iran University of Medical Sciences,Tehran,Iran Seyed Amin Setaredan setarehdan.a@iums.ac.ir 10031947532846001492 10031947532846001492 No Minimally Invasive Surgery Research Center, Iran University of Medical Sciences,Tehran,Iran Fatemeh Soleimany soleimainy.f@iums.ac.ir 10031947532846001493 10031947532846001493 No Department of Biostatistics, Faculty of Public Health, Iran University of Medical Sciences, Tehran, Iran Kimiya Gohari goharikimiya@gmail.com 10031947532846001494 10031947532846001494 No Department of Biostatistics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Amirhossein Aliakbar aliakbar.a@iums.ac.ir 10031947532846001495 10031947532846001495 No Department of Biostatistics, Faculty of Public Health, Iran University of Medical Sciences, Tehran, Iran Negar Zamaninour zamaninour.n@iums.ac.ir 10031947532846001496 10031947532846001496 No Minimally Invasive Surgery Research Center, Iran University of Medical Sciences,Tehran,Iran Abdolreza Pazouki pazouki.a@iums.ac.ir 10031947532846001497 10031947532846001497 No Minimally Invasive Surgery Research Center, Iran University of Medical Sciences,Tehran,Iran. Center of Excellence for Minimally Invasive Surgery Education, Iran University of Medical Sciences Ali Kabir kabir.a@iums.ac.ir 10031947532846001498 10031947532846001498 Yes Minimally Invasive Surgery Research Center, Iran University of Medical Sciences,Tehran,Iran