ObjectivesTo investigate the clinical characteristics and management of plexiform neurofibromas (PNs) in Japanese children with neurofibromatosis 1 (NF1) in the beginning of a new era of treatment with mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor selumetinib. Study designPrimary and secondary surveys were conducted targeting 1612 departments of pediatrics and dermatology in hospitals with ≥300 beds and children's hospitals, which followed up pediatric patients with NF1-associated PN between April 1, 2022, and April 30, 2024, in Japan. ResultsThe response rates in the primary and secondary surveys were 40.4 % and 33.8 %, respectively, and 49 patients were followed up in 23 departments. Their ages at the time ranged from 3.3 to 18.8 years and the onset of PN was most frequently recognized during the first year of life. PN was most often observed superficially in the face (39 %), neck (27 %), and head (24 %), followed by the buttocks (20 %), back (18 %), and thighs (18 %). In addition, PNs could be identified radiologically in the spinal/paraspinal regions (18 %) and pelvis (16 %), where they were rarely visible on the corresponding body surfaces. Major morbidities were cosmetic disfigurement (78 %), pain (53 %), and dysfunction (61 %). Selumetinib use was frequent (69 %) and significantly associated with pain (chi-square test, p = 0.014) and dysfunction (p = 0.014). ConclusionsThis retrospective nationwide study revealed early onset, diverse tumor locations, and varying morbidities in children with NF1-PN, underscoring the need for early evaluation and optimal treatment. A prospective multicenter registry system is warranted to attain better management.