Introduction: Current literature lacks consensus on initial assessments and routine follow-up care of patients with alpha-mannosidosis (AM). A Delphi panel was conducted to generate and validate recommendations on best practices for initial assessment, routine follow-up care, and integrated care coordination of patients with AM., Methods: A modified Delphi method involving 3 rounds of online surveys was used. An independent administrator and 2 nonvoting physician co-chairs managed survey development, anonymous data collection, and analysis. A multidisciplinary panel comprising 20 physicians from 12 countries responded to 57 open-ended questions in the first survey. Round 2 consisted of 11 ranking questions and 44 voting statements. In round 3, panelists voted to validate 60 consensus statements. The panel response rate was ≥95% in all 3 rounds. Panelists used 5-point Likert scales to indicate importance (score of ≥3) or agreement (score of ≥4). Consensus was defined a priori as ≥75% agreement with ≥75% of panelists voting., Results: Consensus was reached on 60 statements, encompassing 3 key areas: initial assessments, routine follow-up care, and treatment-related follow-up. The panel agreed on the type and frequency of assessments related to genetic testing, baseline evaluations, quality of life, biochemical measures, affected body systems, treatment received, and integrated care coordination in patients with AM. Forty-nine statements reached 90% to 100% consensus, 8 statements reached 80% to 85% consensus, and 1 statement reached 75% consensus. Two statements each reached consensus on 15 baseline assessments to be conducted at the initial follow-up visit after diagnosis in pediatric and adult patients., Conclusion: This is the first Delphi study providing internationally applicable, best-practice recommendations for monitoring patients with AM that may improve their care and well-being., Competing Interests: Declaration of competing interest NG is a member of advisory boards and principal investigator for clinical trials. She received consulting fees, research funding, and/or travel reimbursement from BioMarin, Chiesi Farmaceutici S.p.A, Sanofi Genzyme, Takeda, Ultragenyx Pharmaceutical Inc., Regenxbio, JCR Pharma. BKB has received consulting fees and/or honoraria from Alexion, Aro, Astellas, Biomarin, Chiesi, Horizon, JCR Pharma, Jnana, Maze, Moderna, Orchard, Passage Bio, Sanofi, Takeda, Travere, and Ultragenyx. She has conducted clinical trials funded by Biomarin, Denali, Homology Medicines, JCR Pharma, Sangamo, Takeda and Ultragenyx. CF has served as an advisor or consultant for Horizon Therapeutics, Travere, Sanofi Genzyme, Takeda, Avrobio and Chiesi. He has received grants for clinical research from Travere, Passage Bio, REGENXBIO, Sanofi Genzyme, Takeda, JNANA, Denali, and JCR. MM is a member of an advisory board and received consulting fees from BioMarin, Chiesi Farmaceutici S.p.A, Takeda. MGC was a member of an advisory board for Chiesi Farmaceutici S.p.A. MALR does not have any competing interests relative to the subject of this work. PJ is an employee of Nicklaus Childrens Hospital. AML received consulting fees from Alexion, BioMarin, Chiesi Farmaceutici S.p.A., Sanofi Genzyme, and Shire. He has conducted clinical trials for alpha-mannosidosis funded by Chiesi Farmaceutici S.p.A. GT does not have any competing interests relative to the subject of this work. JEGO is a is a member of an advisory board and received consulting fees from Chiesi Farmaceutici S.p.A, Sanofi, Takeda and PTC. KMS is a member of advisory boards and received consulting fees, research funding, and/or travel reimbursement from BioMarin, Chiesi Farmaceutici S.p.A, Sanofi Genzyme, Takeda. CE has been a member of medical advisory boards and received honoraria from Sanofi-Genzyme, Biomarin, Takeda and Amicus Therapeutics. WAH has been an advisory board member for Beam, Zevra, Kriya, Sanofi, and Ultragenyx. RG reports honoraria, consulting fees, speaker fees, research funding, and/or travel reimbursement from Allievex, Amicus, Avrobio, Azafaros, BioMarin, Chiesi, Idorsia, Janssen, JCR, Lysogene, Novartis, Paradigm, Passage Bio, PTC, Regenxbio, Sanofi, Takeda, and Ultragenyx. SSC does not have any competing interests relative to the subject of this work. JBH received consulting fees/speaker honoraria and/or travel expenses from Chiesi Farmaceutici S.p.A., Amicus, Genzyme, and Takeda. CL has received travel grants, speakers fee, and honorarium for advisory boards from BioMarin, Chiesi, Amicus, Alexion, Sanofi, Kyowa Kirin, and Takeda. MMc has consulted and received honoraria in the past 2 years for several pharmaceutical companies including Horizon Therapeutics, Biomarin Pharmaceuticals, Eton Pharmaceuticals, Acer Therapeutics, Ultragenyx, Applied Therapeutics, Jnana Therapeutics, Alexion, and Chiesi. He has been a site PI for clinical trials sponsored by Aeglea Biotherapeutics, Reneo Pharmaceuticals, PTC Therapeutics, Homology Medicines, Horizon Therapeutics, Arcturus Therapeutics, Jnana Therapeutics, Synlogic Therapeutics, and Biomarin Pharmaceutical. FBL does not have any competing interests relative to the subject of this work. MS has received unrestricted grants and travel honoraria from Actelion, Alexion, Azafaros, BioMarin, Chiesi, DENALI, Sanofi Genzyme, Takeda, Ultragenyx, Paradigm, Orchard, and PTC Therapeutics. VRS does not have any competing interests relative to the subject of this work. NM received consulting fees/speaker honoraria and/or travel grants from Amicus, BioMarin, Lysogene, JCR, Orphazyme, Sanofi Genzyme, Takeda, and Chiesi Farmaceutici S.p.A., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)