<p>Genetic testing advancements have improved detection of hereditary polyposis syndromes. Many individuals with unexplained adenomatous polyposis previously underwent limited genetic testing and may benefit from updated testing to identify underlying hereditary polyposis syndromes. We aimed to evaluate the yield of updated testing in adenomatous polyposis cases with previously negative germline genetic testing. Individuals with adenomatous polyposis with uninformative genetic testing prior to 2016 and subsequent updated multi-gene panel testing were analyzed. The updated multi-gene panel testing included the currently recommended 12 polyposis-associated genes. Twenty-one individuals met study criteria. Updated genetic testing identified pathogenic variants (PV) in 6/21 (29%) with four (19%) of the PVs associated with a polyposis phenotype (<i>APC</i> [× 2], <i>AXIN2</i>, and biallelic <i>PMS2</i>) and two (10%) were associated with other cancer predisposition syndromes (<i>ATM</i> and <i>RAD51C</i>). Although <i>APC</i> was included in the initial testing for the two patients found to have <i>APC</i> PVs, the previously completed deletion/duplication analysis did not include the 5′ untranslated region. Updated genetic testing in individuals with unexplained polyposis had a very high yield and identified previously undetected PVs. Updated testing enabled more accurate diagnoses and personalized surveillance recommendations as well as identification of at-risk relatives. Given the improved diagnostic yield, it is crucial to consider genetic testing for individuals with unexplained polyposis who have previously undergone limited testing, due to small gene lists and/or outdated technology, ensuring alignment with current standards.</p>