Hunter syndrome or mucopolysaccharidosis type II (MPSII) is a progressive multisystem X-linked lysosomal storage disease caused by mutations in the IDS gene that shows a wide spectrum of clinical symptoms and severity. Idursulfase, a specific enzyme replacement therapy (ERT) for MPSII, has been available since 2007. ERT, along with symptomatic management of patients, is fundamental for improving patient prognosis and quality of life. The aims of this study were to investigate whether Spanish pediatricians who are experts in managing the disease agreed with current international guidelines regarding MPSII patient diagnosis and follow-up; and to reach a consensus regarding which items are essential for the diagnosis, follow-up, and treatment of these patients in Spain.An advisory panel of 5 experts from the Hunter Spanish Working Group reviewed key studies, developed a questionnaire based on a modified Delphi method, sent the questionnaire to selected experts, and reviewed the responses. The final questionnaire had 83 items in the following categories: diagnosis, ERT considerations after diagnosis, Periodic assessments, and ERT considerations during follow-up. A total of 85 experts were invited to participate; 28 (35%) responded and showed a strong consensus for most items. The advisory panel decided not to perform a second Delphi round. There was strong agreement (>3.1 median value; range, 1 to 4) for 43/56 items in Diagnosis, for 4/6 items in "ERT considerations after diagnosis," for 6/16 items in "Periodic assessments," and for 3/5 items in "ERT considerations during follow-up." Most responses were in agreement with international guidelines, and controversial items were discussed by the advisory panel. Based on the results, on the key studies, and on clinical experience and opinions, the panel developed and scheduled recommendations for the diagnosis and follow-up of patients with MPSII.An expert 5-person panel oversaw a Delphi survey of 28 pediatricians and reached a consensus on recommendations for the diagnosis and follow-up of MPSII patients. This document will help guide clinicians involved in the diagnosis, management, and treatment of MPSII.